Auto merge of #24777 - alexcrichton:musl, r=brson

These commits build on [some great work on reddit](http://www.reddit.com/r/rust/comments/33boew/weekend_experiment_link_rust_programs_against/) for adding MUSL support to the compiler. This goal of this PR is to enable a `--target x86_64-unknown-linux-musl` argument to the compiler to work A-OK. The outcome here is that there are 0 compile-time dependencies for a MUSL-targeting build *except for a linker*. Currently this also assumes that MUSL is being used for statically linked binaries so there is no support for dynamically linked binaries with MUSL.

MUSL support largely just entailed munging around with the linker and where libs are located, and the major highlights are:

* The entirety of `libc.a` is included in `liblibc.rlib` (statically included as an archive).
* The entirety of `libunwind.a` is included in `libstd.rlib` (like with liblibc).
* The target specification for MUSL passes a number of ... flavorful options! Each option is documented in the relevant commit.
* The entire test suite currently passes with MUSL as a target, except for:
  * Dynamic linking tests are all ignored as it's not supported with MUSL
  * Stack overflow detection is not working MUSL yet (I'm not sure why)
* There is a language change included in this PR to add a `target_env` `#[cfg]` directive. This is used to conditionally build code for only MUSL (or for linux distros not MUSL). I highly suspect that this will also be used by Windows to target MSVC instead of a MinGW-based toolchain.

To build a compiler targeting MUSL you need to follow these steps:

1. Clone the current MUSL repo from `git://git.musl-libc.org/musl`. Build this as usual and install it.
2. Clone and build LLVM's [libcxxabi](http://libcxxabi.llvm.org/) library. Only the `libunwind.a` artifact is needed. I have tried using upstream libunwind's source repo but I have not gotten unwinding to work with it unfortunately. Move `libunwind.a` adjacent to MUSL's `libc.a`
3. Configure a Rust checkout with `--target=x86_64-unknown-linux-musl --musl-root=$MUSL_ROOT` where `MUSL_ROOT` is where you installed MUSL in step 1.

I hope to improve building a copy of libunwind as it's still a little sketchy and difficult to do today, but other than that everything should "just work"! This PR is not intended to include 100% comprehensive support for MUSL, as future modifications will probably be necessary.

Author: bors

configure

@@ -583,6 +583,7 @@ valopt jemalloc-root "" "set directory where libjemalloc_pic.a is located"
 valopt build "${DEFAULT_BUILD}" "GNUs ./configure syntax LLVM build triple"
 valopt android-cross-path "/opt/ndk_standalone" "Android NDK standalone path"
 valopt release-channel "dev" "the name of the release channel to build"
+valopt musl-root "/usr/local" "MUSL root installation directory"
 
 # Many of these are saved below during the "writing configuration" step
 # (others are conditionally saved).
@@ -1058,6 +1059,13 @@ do
             fi
             ;;
 
+
+        *-musl)
+            if [ ! -f $CFG_MUSL_ROOT/lib/libc.a ]
+            then
+                err "musl libc $CFG_MUSL_ROOT/lib/libc.a not found"
+            fi
+            ;;
         *)
             ;;
     esac

mk/cfg/aarch64-apple-ios.mk

@@ -20,16 +20,12 @@ CFG_GCCISH_CFLAGS_aarch64-apple-ios := -Wall -Werror -fPIC $(CFG_IOS_SDK_FLAGS_a
 CFG_GCCISH_CXXFLAGS_aarch64-apple-ios := -fno-rtti $(CFG_IOS_SDK_FLAGS_aarch64-apple-ios) -I$(CFG_IOS_SDK_aarch64-apple-ios)/usr/include/c++/4.2.1
 CFG_GCCISH_LINK_FLAGS_aarch64-apple-ios := -lpthread -syslibroot $(CFG_IOS_SDK_aarch64-apple-ios) -Wl,-no_compact_unwind
 CFG_GCCISH_DEF_FLAG_aarch64-apple-ios := -Wl,-exported_symbols_list,
-CFG_GCCISH_PRE_LIB_FLAGS_aarch64-apple-ios :=
-CFG_GCCISH_POST_LIB_FLAGS_aarch64-apple-ios :=
-CFG_DEF_SUFFIX_aarch64-apple-ios := .darwin.def
 CFG_LLC_FLAGS_aarch64-apple-ios := -mattr=+neon,+cyclone,+fp-armv8
 CFG_INSTALL_NAME_aarch64-apple-ios = -Wl,-install_name,@rpath/$(1)
 CFG_LIBUV_LINK_FLAGS_aarch64-apple-ios =
 CFG_EXE_SUFFIX_aarch64-apple-ios :=
 CFG_WINDOWSY_aarch64-apple-ios :=
 CFG_UNIXY_aarch64-apple-ios := 1
-CFG_PATH_MUNGE_aarch64-apple-ios := true
 CFG_LDPATH_aarch64-apple-ios :=
 CFG_RUN_aarch64-apple-ios = $(2)
 CFG_RUN_TARG_aarch64-apple-ios = $(call CFG_RUN_aarch64-apple-ios,,$(2))

mk/cfg/aarch64-linux-android.mk

@@ -13,15 +13,11 @@ CFG_GCCISH_CFLAGS_aarch64-linux-android := -Wall -g -fPIC -D__aarch64__ -DANDROI
 CFG_GCCISH_CXXFLAGS_aarch64-linux-android := -fno-rtti $(CXXFLAGS)
 CFG_GCCISH_LINK_FLAGS_aarch64-linux-android := -shared -fPIC -ldl -g -lm -lsupc++
 CFG_GCCISH_DEF_FLAG_aarch64-linux-android := -Wl,--export-dynamic,--dynamic-list=
-CFG_GCCISH_PRE_LIB_FLAGS_aarch64-linux-android := -Wl,-whole-archive
-CFG_GCCISH_POST_LIB_FLAGS_aarch64-linux-android := -Wl,-no-whole-archive
-CFG_DEF_SUFFIX_aarch64-linux-android := .android.def
 CFG_LLC_FLAGS_aarch64-linux-android :=
 CFG_INSTALL_NAME_aarch64-linux-android =
 CFG_EXE_SUFFIX_aarch64-linux-android :=
 CFG_WINDOWSY_aarch64-linux-android :=
 CFG_UNIXY_aarch64-linux-android := 1
-CFG_PATH_MUNGE_aarch64-linux-android := true
 CFG_LDPATH_aarch64-linux-android :=
 CFG_RUN_aarch64-linux-android=
 CFG_RUN_TARG_aarch64-linux-android=

mk/cfg/aarch64-unknown-linux-gnu.mk

@@ -13,15 +13,11 @@ CFG_GCCISH_CFLAGS_aarch64-unknown-linux-gnu := -Wall -g -fPIC -D__aarch64__ $(CF
 CFG_GCCISH_CXXFLAGS_aarch64-unknown-linux-gnu := -fno-rtti $(CXXFLAGS)
 CFG_GCCISH_LINK_FLAGS_aarch64-unknown-linux-gnu := -shared -fPIC -g
 CFG_GCCISH_DEF_FLAG_aarch64-unknown-linux-gnu := -Wl,--export-dynamic,--dynamic-list=
-CFG_GCCISH_PRE_LIB_FLAGS_aarch64-unknown-linux-gnu := -Wl,-whole-archive
-CFG_GCCISH_POST_LIB_FLAGS_aarch64-unknown-linux-gnu := -Wl,-no-whole-archive
-CFG_DEF_SUFFIX_aarch64-unknown-linux-gnu := .linux.def
 CFG_LLC_FLAGS_aarch64-unknown-linux-gnu :=
 CFG_INSTALL_NAME_aarch64-unknown-linux-gnu =
 CFG_EXE_SUFFIX_aarch64-unknown-linux-gnu :=
 CFG_WINDOWSY_aarch64-unknown-linux-gnu :=
 CFG_UNIXY_aarch64-unknown-linux-gnu := 1
-CFG_PATH_MUNGE_aarch64-unknown-linux-gnu := true
 CFG_LDPATH_aarch64-unknown-linux-gnu :=
 CFG_RUN_aarch64-unknown-linux-gnu=$(2)
 CFG_RUN_TARG_aarch64-unknown-linux-gnu=$(call CFG_RUN_aarch64-unknown-linux-gnu,,$(2))

mk/cfg/arm-linux-androideabi.mk

@@ -12,15 +12,11 @@ CFG_GCCISH_CFLAGS_arm-linux-androideabi := -Wall -g -fPIC -D__arm__ -DANDROID -D
 CFG_GCCISH_CXXFLAGS_arm-linux-androideabi := -fno-rtti $(CXXFLAGS)
 CFG_GCCISH_LINK_FLAGS_arm-linux-androideabi := -shared -fPIC -ldl -g -lm -lsupc++
 CFG_GCCISH_DEF_FLAG_arm-linux-androideabi := -Wl,--export-dynamic,--dynamic-list=
-CFG_GCCISH_PRE_LIB_FLAGS_arm-linux-androideabi := -Wl,-whole-archive
-CFG_GCCISH_POST_LIB_FLAGS_arm-linux-androideabi := -Wl,-no-whole-archive
-CFG_DEF_SUFFIX_arm-linux-androideabi := .android.def
 CFG_LLC_FLAGS_arm-linux-androideabi :=
 CFG_INSTALL_NAME_arm-linux-androideabi =
 CFG_EXE_SUFFIX_arm-linux-androideabi :=
 CFG_WINDOWSY_arm-linux-androideabi :=
 CFG_UNIXY_arm-linux-androideabi := 1
-CFG_PATH_MUNGE_arm-linux-androideabi := true
 CFG_LDPATH_arm-linux-androideabi :=
 CFG_RUN_arm-linux-androideabi=
 CFG_RUN_TARG_arm-linux-androideabi=

mk/cfg/arm-unknown-linux-gnueabi.mk

@@ -13,15 +13,11 @@ CFG_GCCISH_CFLAGS_arm-unknown-linux-gnueabi := -Wall -g -fPIC -D__arm__ -mfpu=vf
 CFG_GCCISH_CXXFLAGS_arm-unknown-linux-gnueabi := -fno-rtti $(CXXFLAGS)
 CFG_GCCISH_LINK_FLAGS_arm-unknown-linux-gnueabi := -shared -fPIC -g
 CFG_GCCISH_DEF_FLAG_arm-unknown-linux-gnueabi := -Wl,--export-dynamic,--dynamic-list=
-CFG_GCCISH_PRE_LIB_FLAGS_arm-unknown-linux-gnueabi := -Wl,-whole-archive
-CFG_GCCISH_POST_LIB_FLAGS_arm-unknown-linux-gnueabi := -Wl,-no-whole-archive
-CFG_DEF_SUFFIX_arm-unknown-linux-gnueabi := .linux.def
 CFG_LLC_FLAGS_arm-unknown-linux-gnueabi :=
 CFG_INSTALL_NAME_arm-unknown-linux-gnueabi =
 CFG_EXE_SUFFIX_arm-unknown-linux-gnueabi :=
 CFG_WINDOWSY_arm-unknown-linux-gnueabi :=
 CFG_UNIXY_arm-unknown-linux-gnueabi := 1
-CFG_PATH_MUNGE_arm-unknown-linux-gnueabi := true
 CFG_LDPATH_arm-unknown-linux-gnueabi :=
 CFG_RUN_arm-unknown-linux-gnueabi=$(2)
 CFG_RUN_TARG_arm-unknown-linux-gnueabi=$(call CFG_RUN_arm-unknown-linux-gnueabi,,$(2))

mk/cfg/arm-unknown-linux-gnueabihf.mk

@@ -13,15 +13,11 @@ CFG_GCCISH_CFLAGS_arm-unknown-linux-gnueabihf := -Wall -g -fPIC -D__arm__ $(CFLA
 CFG_GCCISH_CXXFLAGS_arm-unknown-linux-gnueabihf := -fno-rtti $(CXXFLAGS)
 CFG_GCCISH_LINK_FLAGS_arm-unknown-linux-gnueabihf := -shared -fPIC -g
 CFG_GCCISH_DEF_FLAG_arm-unknown-linux-gnueabihf := -Wl,--export-dynamic,--dynamic-list=
-CFG_GCCISH_PRE_LIB_FLAGS_arm-unknown-linux-gnueabihf := -Wl,-whole-archive
-CFG_GCCISH_POST_LIB_FLAGS_arm-unknown-linux-gnueabihf := -Wl,-no-whole-archive
-CFG_DEF_SUFFIX_arm-unknown-linux-gnueabihf := .linux.def
 CFG_LLC_FLAGS_arm-unknown-linux-gnueabihf :=
 CFG_INSTALL_NAME_ar,-unknown-linux-gnueabihf =
 CFG_EXE_SUFFIX_arm-unknown-linux-gnueabihf :=
 CFG_WINDOWSY_arm-unknown-linux-gnueabihf :=
 CFG_UNIXY_arm-unknown-linux-gnueabihf := 1
-CFG_PATH_MUNGE_arm-unknown-linux-gnueabihf := true
 CFG_LDPATH_arm-unknown-linux-gnueabihf :=
 CFG_RUN_arm-unknown-linux-gnueabihf=$(2)
 CFG_RUN_TARG_arm-unknown-linux-gnueabihf=$(call CFG_RUN_arm-unknown-linux-gnueabihf,,$(2))

mk/cfg/armv7-apple-ios.mk

@@ -19,15 +19,11 @@ CFG_GCCISH_CFLAGS_armv7-apple-ios := -Wall -Werror -g -fPIC $(CFG_IOS_SDK_FLAGS_
 CFG_GCCISH_CXXFLAGS_armv7-apple-ios := -fno-rtti $(CFG_IOS_SDK_FLAGS_armv7-apple-ios) -I$(CFG_IOS_SDK_armv7-apple-ios)/usr/include/c++/4.2.1
 CFG_GCCISH_LINK_FLAGS_armv7-apple-ios := -lpthread -syslibroot $(CFG_IOS_SDK_armv7-apple-ios) -Wl,-no_compact_unwind
 CFG_GCCISH_DEF_FLAG_armv7-apple-ios := -Wl,-exported_symbols_list,
-CFG_GCCISH_PRE_LIB_FLAGS_armv7-apple-ios :=
-CFG_GCCISH_POST_LIB_FLAGS_armv7-apple-ios :=
-CFG_DEF_SUFFIX_armv7-apple-ios := .darwin.def
 CFG_LLC_FLAGS_armv7-apple-ios := -mattr=+vfp3,+v7,+neon -march=arm
 CFG_INSTALL_NAME_armv7-apple-ios = -Wl,-install_name,@rpath/$(1)
 CFG_EXE_SUFFIX_armv7-apple-ios :=
 CFG_WINDOWSY_armv7-apple-ios :=
 CFG_UNIXY_armv7-apple-ios := 1
-CFG_PATH_MUNGE_armv7-apple-ios := true
 CFG_LDPATH_armv7-apple-ios :=
 CFG_RUN_armv7-apple-ios = $(2)
 CFG_RUN_TARG_armv7-apple-ios = $(call CFG_RUN_armv7-apple-ios,,$(2))

mk/cfg/armv7s-apple-ios.mk

@@ -19,15 +19,11 @@ CFG_GCCISH_CFLAGS_armv7s-apple-ios := -Wall -Werror -g -fPIC $(CFG_IOS_SDK_FLAGS
 CFG_GCCISH_CXXFLAGS_armv7s-apple-ios := -fno-rtti $(CFG_IOS_SDK_FLAGS_armv7s-apple-ios) -I$(CFG_IOS_SDK_armv7s-apple-ios)/usr/include/c++/4.2.1
 CFG_GCCISH_LINK_FLAGS_armv7s-apple-ios := -lpthread -syslibroot $(CFG_IOS_SDK_armv7s-apple-ios) -Wl,-no_compact_unwind
 CFG_GCCISH_DEF_FLAG_armv7s-apple-ios := -Wl,-exported_symbols_list,
-CFG_GCCISH_PRE_LIB_FLAGS_armv7s-apple-ios :=
-CFG_GCCISH_POST_LIB_FLAGS_armv7s-apple-ios :=
-CFG_DEF_SUFFIX_armv7s-apple-ios := .darwin.def
 CFG_LLC_FLAGS_armv7s-apple-ios := -mattr=+vfp4,+v7,+neon
 CFG_INSTALL_NAME_armv7s-apple-ios = -Wl,-install_name,@rpath/$(1)
 CFG_EXE_SUFFIX_armv7s-apple-ios :=
 CFG_WINDOWSY_armv7s-apple-ios :=
 CFG_UNIXY_armv7s-apple-ios := 1
-CFG_PATH_MUNGE_armv7s-apple-ios := true
 CFG_LDPATH_armv7s-apple-ios :=
 CFG_RUN_armv7s-apple-ios = $(2)
 CFG_RUN_TARG_armv7s-apple-ios = $(call CFG_RUN_armv7s-apple-ios,,$(2))

mk/cfg/i386-apple-ios.mk

@@ -18,15 +18,11 @@ CFG_GCCISH_CFLAGS_i386-apple-ios := -Wall -Werror -g -fPIC -m32 $(CFG_IOSSIM_FLA
 CFG_GCCISH_CXXFLAGS_i386-apple-ios := -fno-rtti $(CFG_IOSSIM_FLAGS_i386-apple-ios) -I$(CFG_IOSSIM_SDK_i386-apple-ios)/usr/include/c++/4.2.1
 CFG_GCCISH_LINK_FLAGS_i386-apple-ios := -lpthread -m32 -Wl,-no_compact_unwind -m32 -Wl,-syslibroot $(CFG_IOSSIM_SDK_i386-apple-ios)
 CFG_GCCISH_DEF_FLAG_i386-apple-ios := -Wl,-exported_symbols_list,
-CFG_GCCISH_PRE_LIB_FLAGS_i386-apple-ios :=
-CFG_GCCISH_POST_LIB_FLAGS_i386-apple-ios :=
-CFG_DEF_SUFFIX_i386-apple-ios := .darwin.def
 CFG_LLC_FLAGS_i386-apple-ios =
 CFG_INSTALL_NAME_i386-apple-ios = -Wl,-install_name,@rpath/$(1)
 CFG_EXE_SUFFIX_i386-apple-ios :=
 CFG_WINDOWSY_i386-apple-ios :=
 CFG_UNIXY_i386-apple-ios := 1
-CFG_PATH_MUNGE_i386-apple-ios = :true
 CFG_LDPATH_i386-apple-ios =
 CFG_RUN_i386-apple-ios = $(2)
 CFG_RUN_TARG_i386-apple-ios = $(call CFG_RUN_i386-apple-ios,,$(2))