ninja check-flang-rt is broken on LLVM 21 Windows Release

[omjavaid]

When building LLVM 21.1.0-rc1 (release/21.x) for Windows ARM64, the ninja check-flang-rt target fails with linker errors due to a mismatch in RuntimeLibrary settings.

Using build script from #131687 as flang-rt required RUNTIMES build.

error.log

@zmodem FYI ^

@zmodem is it possible to include flang in LLVM 21 x64 Windows release?

[llvmbot]

@llvm/issue-subscribers-flang-runtime

Author: Omair Javaid (omjavaid)

When building LLVM 21.1.0-rc1 (release/21.x) for Windows ARM64, the `ninja check-flang-rt` target fails with linker errors due to a mismatch in RuntimeLibrary settings.

Using build script from #131687 as flang-rt required RUNTIMES build.

error.log

@zmodem FYI ^

@zmodem is it possible to include flang in LLVM 21 x64 Windows release?

[DavidTruby]

This looks like the flang-rt tests are not getting built with the same --fms-runtime-lib= flag as the flang-rt build itself. I'm not sure why this might be happening but I will look in to it.

[DavidTruby]

The exact issue seems to be that LLVM_ENABLE_RPMALLOC (used in the script) sets the CMAKE_MSVC_RUNTIME_LIBRARY to MultiThreaded instead of MultiThreadedDLL, but in the flang-rt tests we're assuming that it's MultiThreadedDLL. So that's causing check-flang-rt to fail. I'll look into fixing this.

[DavidTruby]

@omjavaid I think that #152318 fixes this issue; would you be able to apply that patch and try the script again and see if it works for you?