[compiler-rt][asan] Silence warning

This would silence:
```
[2003/2029] Generating ASAN_NOINST_TEST_OBJECTS.asan_noinst_test.cpp.x86_64-inline.o
In file included from C:/git/llvm-project/compiler-rt/lib/asan/tests/asan_noinst_test.cpp:24:
In file included from C:/git/llvm-project/compiler-rt/lib/asan\asan_allocator.h:20:
In file included from C:/git/llvm-project/compiler-rt/lib\sanitizer_common/sanitizer_allocator.h:74:
C:/git/llvm-project/compiler-rt/lib\sanitizer_common\sanitizer_allocator_primary64.h:639:54: warning: 'static_assert' with no message is a C++17 extension [-Wc++17-extensions]
  639 |   static_assert(kRegionSize >= SizeClassMap::kMaxSize);
      |                                                      ^
      |                                                      , ""
1 warning generated.
```