[compiler-rt] [compiler-rt] fix gcc <13 support by removing enum-type-specifier (PR #165034)

[Saleem Abdulrasool via llvm-commits]

compnerd wrote:

This isn't fine sadly - the signedness is platform specific. This needs to be preserved. I think that requiring GCC 7+ is acceptable.

https://github.com/llvm/llvm-project/pull/165034