Partially revert 9d342d5 (#19)

Context: #10
Context: 9d342d5
Context: dotnet/android#8806 (comment)

Revert the portion of 9d342d5 which modified the way command-line
arguments are parsed.  The `cxxopt` C++ library that was used turns out
not to support some GNU-style options (e.g. `-mfpu=vpf3`) which breaks
the MonoAOT compiler that uses them.

Instead, copy `getopt.c` (BSD 2-clause + MIT/X11 licenses) and
`getopt.h` (Public Domain license) implementations from the MinGW
project and use `getopt` across all platforms.

Additionally, fix generation of the artifact package by making sure that
all the executable files are, in fact, executable by setting the correct
permissions.

Author: grendello

package.sh

@@ -107,6 +107,7 @@ function prepare()
 		else
 			cp -P -a "${artifacts_source_bin}/${b}" "${artifacts_dest_bin}/${dest_b}"
 		fi
+		chmod 755 "${artifacts_dest_bin}/${dest_b}"
 
 		if [ -n "${src_pdb}" -a -f "${artifacts_source_bin}/${src_pdb}" ]; then
 			cp -P -a "${artifacts_source_bin}/${src_pdb}" "${artifacts_dest_bin}/${dest_pdb}"

src/compat-include/getopt.h

@@ -0,0 +1,97 @@
+#ifndef __GETOPT_H__
+/**
+ * DISCLAIMER
+ * This file has no copyright assigned and is placed in the Public Domain.
+ * This file is part of the mingw-w64 runtime package.
+ *
+ * The mingw-w64 runtime package and its code is distributed in the hope that it 
+ * will be useful but WITHOUT ANY WARRANTY.  ALL WARRANTIES, EXPRESSED OR 
+ * IMPLIED ARE HEREBY DISCLAIMED.  This includes but is not limited to 
+ * warranties of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+#define __GETOPT_H__
+
+/* All the headers include this file. */
+#include <crtdefs.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern int optind;		/* index of first non-option in argv      */
+extern int optopt;		/* single option character, as parsed     */
+extern int opterr;		/* flag to enable built-in diagnostics... */
+				/* (user may set to zero, to suppress)    */
+
+extern char *optarg;		/* pointer to argument of current option  */
+
+extern int getopt(int nargc, char * const *nargv, const char *options);
+
+#ifdef __cplusplus
+}
+#endif
+/*
+ * POSIX requires the `getopt' API to be specified in `unistd.h';
+ * thus, `unistd.h' includes this header.  However, we do not want
+ * to expose the `getopt_long' or `getopt_long_only' APIs, when
+ * included in this manner.  Thus, close the standard __GETOPT_H__
+ * declarations block, and open an additional __GETOPT_LONG_H__
+ * specific block, only when *not* __UNISTD_H_SOURCED__, in which
+ * to declare the extended API.
+ */
+#endif /* !defined(__GETOPT_H__) */
+
+#if !defined(__GETOPT_BSD_H__) && defined(_BSD_SOURCE)
+#define __GETOPT_BSD_H__
+/*
+ * BSD adds the non-standard `optreset' feature, for reinitialisation
+ * of `getopt' parsing.  We support this feature, for applications which
+ * proclaim their BSD heritage, before including this header; however,
+ * to maintain portability, developers are advised to avoid it.
+ */
+# define optreset  __mingw_optreset
+extern int optreset;
+#endif /* !defined(__GETOPT_BSD_H__) && defined(_BSD_SOURCE) */
+
+#if !defined(__UNISTD_H_SOURCED__) && !defined(__GETOPT_LONG_H__)
+#define __GETOPT_LONG_H__
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct option		/* specification for a long form option...	*/
+{
+  const char *name;		/* option name, without leading hyphens */
+  int         has_arg;		/* does it take an argument?		*/
+  int        *flag;		/* where to save its status, or NULL	*/
+  int         val;		/* its associated status value		*/
+};
+
+enum    		/* permitted values for its `has_arg' field...	*/
+{
+  no_argument = 0,      	/* option never takes an argument	*/
+  required_argument,		/* option always requires an argument	*/
+  optional_argument		/* option may take an argument		*/
+};
+
+extern int getopt_long(int nargc, char * const *nargv, const char *options,
+    const struct option *long_options, int *idx);
+extern int getopt_long_only(int nargc, char * const *nargv, const char *options,
+    const struct option *long_options, int *idx);
+/*
+ * Previous MinGW implementation had...
+ */
+#ifndef HAVE_DECL_GETOPT
+/*
+ * ...for the long form API only; keep this for compatibility.
+ */
+# define HAVE_DECL_GETOPT	1
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* !defined(__UNISTD_H_SOURCED__) && !defined(__GETOPT_LONG_H__) */