[Windows on Arm] Add env var for msvc compatibility option

[DavidSpickett]

Summary

We are using clang 14.0.5 which has a default version of 19.26.

This adds use of an env var MSVC_VER that we'll set on our
side for this and future updates as the clang-cl version
doesn't always track what llvm needs to build.

[DavidSpickett]

See https://lab.llvm.org/buildbot/#/builders/65/builds/6373

CMake Error at cmake/modules/CheckCompilerVersion.cmake:69 (message):
  Host Clang must have at least -fms-compatibility-version=19.27, your
  version is 19.26.

We have been giving this option to clang-13 for local builds and haven't seen any issues so it's pretty low risk and 15.0.0 is too far away to leave the bots red IMO.

[rovka]

LGTM. Do you think we should use an environment variable instead, so we can just change it on the machine in the future (rather than going through zorg again)? We're doing something similar a few lines down with the path to the builtins library (needed by flang).

[DavidSpickett]

Use MSVC_VER env var instead.

[DavidSpickett]

@rovka Does the env var version look good to you?

[DavidSpickett]

Landed as https://github.com/llvm/llvm-zorg/commit/e540c3f0253358d9712ef1ba9b792c763057f697.

buildbot/osuosl/master/config/builders.py

'factory' : ClangBuilder.getClangCMakeBuildFactory(
                     checkout_flang=True,
                     # Only enabling checks we expect to work.
                     checks=['check-flang'],
                     extra_cmake_args=[
                         "-DCMAKE_TRY_COMPILE_CONFIGURATION=Release",
                         "-DLLVM_DEFAULT_TARGET_TRIPLE=aarch64-pc-windows-msvc",
                         "-DLLVM_HOST_TRIPLE=aarch64-pc-windows-msvc",
                         "-DLLVM_TARGET_ARCH=AArch64",
+                        # The MSVC_VER environment variable is expected to already exist
+                        # on the worker when it is launched.
+                        "-DCMAKE_C_FLAGS='-fms-compatibility-version=%MSVC_VER%'",
+                        "-DCMAKE_CXX_FLAGS='-fms-compatibility-version=%MSVC_VER%'",
                         # The BUILTINS environment variable is expected to already exist
                         # on the worker when it is launched.
                         "-DCMAKE_EXE_LINKER_FLAGS=%BUILTINS%",
                         "-DCMAKE_SHARED_LINKER_FLAGS=%BUILTINS%",
                         "-DCMAKE_STATIC_LINKER_FLAGS=%BUILTINS%",
                         "-DCMAKE_MODULE_LINKER_FLAGS=%BUILTINS%",
                         # FIXME: compiler-rt\lib\sanitizer_common\sanitizer_unwind_win.cpp assumes WIN64 is x86_64,
                         #        so, before that's fixed, disable everything that triggers its build.
'factory' : ClangBuilder.getClangCMakeBuildFactory(
                     checks=[], # Disable testing until MCJIT failures are fixed
                     useTwoStage=True,
                     testStage1=False,
                     extra_cmake_args=[
                         "-DCMAKE_TRY_COMPILE_CONFIGURATION=Release",
                         "-DLLVM_DEFAULT_TARGET_TRIPLE=aarch64-pc-windows-msvc",
                         "-DLLVM_HOST_TRIPLE=aarch64-pc-windows-msvc",
                         "-DLLVM_TARGET_ARCH=AArch64",
+                        # The MSVC_VER environment variable is expected to already exist
+                        # on the worker when it is launched.
+                        "-DCMAKE_C_FLAGS='-fms-compatibility-version=%MSVC_VER%'",
+                        "-DCMAKE_CXX_FLAGS='-fms-compatibility-version=%MSVC_VER%'",
                         # FIXME: compiler-rt\lib\sanitizer_common\sanitizer_unwind_win.cpp assumes WIN64 is x86_64,
                         #        so, before that's fixed, disable everything that triggers its build.
                         "-DCOMPILER_RT_BUILD_SANITIZERS=OFF",
                         "-DCOMPILER_RT_BUILD_MEMPROF=OFF",
                         "-DCOMPILER_RT_BUILD_XRAY=OFF"])},
 
     {'name' : 'clang-x64-windows-msvc',
     'tags'  : ["clang"],