Cannot build on macOS if adding -mavx / -mavx2 to global build flags

[jcelerier]

Repro:

$ clang++ -DHAVE_CONFIG_H -I/Users/jcelerier/build-score-qt_rhi-Debug/3rdparty/snappy -I/Users/jcelerier/score/3rdparty/snappy  -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk   -c /Users/jcelerier/score/3rdparty/snappy/snappy.cc -mssse3 -mavx2 -std=c++20

/Users/jcelerier/score/3rdparty/snappy/snappy.cc:1242:3: error: unknown type name '__m256i'
  __m256i data = _mm256_lddqu_si256(static_cast<const __m256i *>(src));
  ^
/Users/jcelerier/score/3rdparty/snappy/snappy.cc:1242:55: error: unknown type name '__m256i'
  __m256i data = _mm256_lddqu_si256(static_cast<const __m256i *>(src));
                                                      ^
/Users/jcelerier/score/3rdparty/snappy/snappy.cc:1242:18: error: use of undeclared identifier '_mm256_lddqu_si256'; did you mean '_mm_lddqu_si128'?
  __m256i data = _mm256_lddqu_si256(static_cast<const __m256i *>(src));
                 ^~~~~~~~~~~~~~~~~~
                 _mm_lddqu_si128

It works if I add

#include <x86intrin.h>

at the top of snappy-internal.h:

#if SNAPPY_HAVE_SSSE3
// Please do not replace with <x86intrin.h> or with headers that assume more
// advanced SSE versions without checking with all the OWNERS.
#include <emmintrin.h>
#include <tmmintrin.h>
#include <x86intrin.h>
#endif 

Apple clang version 15.0.0 (clang-1500.3.9.4)
Target: x86_64-apple-darwin24.0.0