I'm building a library that extensively uses fmt for it's debugging and error system, and on MacOS the build fails with the following error in my actions builds. The project uses C++20 and adds fmt as a subdirectory. It appears to be a clang specific problem.

/Users/runner/work/VkBootstrap3/VkBootstrap3/external/fmt/include/fmt/base.h:401:1: warning: unknown warning group '-Wbit-int-extension', ignored [-Wunknown-warning-option]
FMT_PRAGMA_CLANG(diagnostic ignored "-Wbit-int-extension")

/Users/runner/work/VkBootstrap3/VkBootstrap3/external/fmt/include/fmt/base.h:402:33: error: unknown type name '_BitInt'
template <int N> using bitint = _BitInt(N);

The error then seems to cascade down and cause many other errors in the file, but it appears to be centered around this one. I'm sure it's probably some error on my end, but multiple separate pieces have this error, so I'm not sure where it comes from.