Bug 1523003 - Remove the force-ms-compatibility for clang-cl. r=glandium

build/moz.configure/toolchain.configure

@@ -619,13 +619,6 @@ def check_compiler(compiler, language, target):
         elif info.type == 'clang-cl' and info.language_version != cxx14_version:
             append_flag('-std=c++14')
 
-    # We force clang-cl to emulate Visual C++ 2017 version 15.8.4
-    msvc_version = '19.15.26726'
-    if info.type == 'clang-cl' and info.version != msvc_version:
-        # This flag is a direct clang-cl flag that doesn't need -Xclang,
-        # add it directly.
-        flags.append('-fms-compatibility-version=%s' % msvc_version)
-
     # Check compiler target
     # --------------------------------------------------------------------
     if not info.cpu or info.cpu != target.cpu:

python/mozbuild/mozbuild/test/configure/test_toolchain_configure.py

@@ -263,7 +263,6 @@ CLANG_CL_3_9 = (CLANG_BASE('3.9.0') + VS('18.00.00000') + DEFAULT_C11 +
         '__STDC_VERSION__': False,
         '__cplusplus': '201103L',
     },
-    '-fms-compatibility-version=19.15.26726': VS('19.15.26726')[None],
 }
 
 CLANG_CL_PLATFORM_X86 = FakeCompiler(VS_PLATFORM_X86, GCC_PLATFORM_X86[None])
@@ -928,17 +927,15 @@ class WindowsToolchainTest(BaseToolchainTest):
         language='C++',
     )
     CLANG_CL_3_9_RESULT = CompilerResult(
-        flags=['-Xclang', '-std=gnu99',
-               '-fms-compatibility-version=19.15.26726'],
-        version='19.15.26726',
+        flags=['-Xclang', '-std=gnu99'],
+        version='3.9.0',
         type='clang-cl',
         compiler='/usr/bin/clang-cl',
         language='C',
     )
     CLANGXX_CL_3_9_RESULT = CompilerResult(
-        flags=['-Xclang', '-std=c++14',
-               '-fms-compatibility-version=19.15.26726'],
-        version='19.15.26726',
+        flags=['-Xclang', '-std=c++14'],
+        version='3.9.0',
         type='clang-cl',
         compiler='/usr/bin/clang-cl',
         language='C++',