The typedef seems to be pulled in coincidentally with newer SDKs, but
older ones need to import the header explicitly.
(cherry picked from commit d2910904fb)
Don't rely on checking __clang_major__ since it is not comparable
between different vendors. Don't use "#pragma clang attribute" since it
is only available in relatively recent versions, there's no obvious way
to check if it's supported, and just using __attribute__ directly (for
gcc as well) results in simpler code anyway.
The __clang_major__ and __clang_minor__ macros provide a marketing
version, which is not necessarily comparable for clang distributions
from different vendors[1]. In practice, the versioning scheme for
Apple's clang is indeed completely different to that of the llvm.org
releases. It is thus preferable to check for features directly rather
than comparing versions.
In this specific case, __builtin_bswap16 was being used with older
Apple clang versions that don't support it.
[1] https://clang.llvm.org/docs/LanguageExtensions.html#builtin-macros
Joshua Root