disable `-Wmicrosoft-enum-value` and `-Wlanguage-extension-token`

[solomoncyj]

compiling on windows will cause clang to emit messages that seem to be normal behavior, eg:

[3694/3772] Building CXX object tools/sancov/CMakeFiles/sancov.dir/sancov.cpp.obj
In file included from C:/Users/solom/Downloads/llvm-project/llvm/tools/sancov/sancov.cpp:11:
In file included from C:/Users/solom/Downloads/llvm-project/llvm/include\llvm/ADT/STLExtras.h:21:
In file included from C:/Users/solom/Downloads/llvm-project/llvm/include\llvm/ADT/Hashing.h:49:
In file included from C:/Users/solom/Downloads/llvm-project/llvm/include\llvm/Support/DataTypes.h:19:
C:/Users/solom/Downloads/llvm-project/llvm/include\llvm-c/DataTypes.h:62:16: warning: extension used [-Wlanguage-extension-token]
   62 | typedef signed __int64 ssize_t;
      |                ^
In file included from C:/Users/solom/Downloads/llvm-project/llvm/tools/sancov/sancov.cpp:11:
In file included from C:/Users/solom/Downloads/llvm-project/llvm/include\llvm/ADT/STLExtras.h:21:
In file included from C:/Users/solom/Downloads/llvm-project/llvm/include\llvm/ADT/Hashing.h:51:
In file included from C:/Users/solom/Downloads/llvm-project/llvm/include\llvm/Support/SwapByteOrder.h:18:
C:/Users/solom/Downloads/llvm-project/llvm/include\llvm/ADT/bit.h:63:65: warning: extension used [-Wlanguage-extension-token]
   63 | unsigned char _BitScanForward64(unsigned long *_Index, unsigned __int64 _Mask);
      |                                                                 ^
C:/Users/solom/Downloads/llvm-project/llvm/include\llvm/ADT/bit.h:65:65: warning: extension used [-Wlanguage-extension-token]
   65 | unsigned char _BitScanReverse64(unsigned long *_Index, unsigned __int64 _Mask);
      |                                                                 ^
In file included from C:/Users/solom/Downloads/llvm-project/llvm/tools/sancov/sancov.cpp:30:
In file included from C:/Users/solom/Downloads/llvm-project/llvm/include\llvm/Object/MachO.h:23:
C:/Users/solom/Downloads/llvm-project/llvm/include\llvm/BinaryFormat/MachO.h:88:3: warning: enumerator value is not representable in the underlying type 'int' [-Wmicrosoft-enum-value]
   88 |   MH_DYLIB_IN_CACHE = 0x80000000u,
      |   ^
C:/Users/solom/Downloads/llvm-project/llvm/include\llvm/BinaryFormat/MachO.h:2274:3: warning: enumerator value is not representable in the underlying type 'int' [-Wmicrosoft-enum-value]
 2274 |   CS_DATAVAULT_CONTROLLER =
      |   ^
C:/Users/solom/Downloads/llvm-project/llvm/include\llvm/BinaryFormat/MachO.h:2298:3: warning: enumerator value is not representable in the underlying type 'int' [-Wmicrosoft-enum-value]
 2298 |   CSMAGIC_REQUIREMENT = 0xfade0c00, /* single Requirement blob */
      |   ^
C:/Users/solom/Downloads/llvm-project/llvm/include\llvm/BinaryFormat/MachO.h:2299:3: warning: enumerator value is not representable in the underlying type 'int' [-Wmicrosoft-enum-value]
 2299 |   CSMAGIC_REQUIREMENTS =
      |   ^
C:/Users/solom/Downloads/llvm-project/llvm/include\llvm/BinaryFormat/MachO.h:2301:3: warning: enumerator value is not representable in the underlying type 'int' [-Wmicrosoft-enum-value]
 2301 |   CSMAGIC_CODEDIRECTORY = 0xfade0c02,      /* CodeDirectory blob */
      |   ^
C:/Users/solom/Downloads/llvm-project/llvm/include\llvm/BinaryFormat/MachO.h:2302:3: warning: enumerator value is not representable in the underlying type 'int' [-Wmicrosoft-enum-value]
 2302 |   CSMAGIC_EMBEDDED_SIGNATURE = 0xfade0cc0, /* embedded form of signature data */
      |   ^
C:/Users/solom/Downloads/llvm-project/llvm/include\llvm/BinaryFormat/MachO.h:2303:3: warning: enumerator value is not representable in the underlying type 'int' [-Wmicrosoft-enum-value]
 2303 |   CSMAGIC_EMBEDDED_SIGNATURE_OLD = 0xfade0b02, /* XXX */
      |   ^
C:/Users/solom/Downloads/llvm-project/llvm/include\llvm/BinaryFormat/MachO.h:2304:3: warning: enumerator value is not representable in the underlying type 'int' [-Wmicrosoft-enum-value]
 2304 |   CSMAGIC_EMBEDDED_ENTITLEMENTS = 0xfade7171,  /* embedded entitlements */
      |   ^
C:/Users/solom/Downloads/llvm-project/llvm/include\llvm/BinaryFormat/MachO.h:2305:3: warning: enumerator value is not representable in the underlying type 'int' [-Wmicrosoft-enum-value]
 2305 |   CSMAGIC_DETACHED_SIGNATURE =
      |   ^
C:/Users/solom/Downloads/llvm-project/llvm/include\llvm/BinaryFormat/MachO.h:2307:3: warning: enumerator value is not representable in the underlying type 'int' [-Wmicrosoft-enum-value]
 2307 |   CSMAGIC_BLOBWRAPPER = 0xfade0b01, /* CMS Signature, among other things */
      |   ^
13 warnings generated.

[AaronBallman]

The ones about __int64_t are valid diagnostics; we are using that extension in MSVC mode. If we want to silence those diagnostics, we need to treat those declarations as part of the system headers because they're manually written so as to avoid including the system header.

The ones about the enumerator value not fitting within int seem just... wrong... to me: https://godbolt.org/z/E3rq3GKG4

[AaronBallman]

Oh! It's because the high bit is set. That is a duplicate of #32922

[solomoncyj]

I was thinking to disable the flag if it is expected behaviour as it will pollute the build output