[compiler-rt] [tsan] Fix alignas specifier in tsan_platform_mac.cpp (PR #99252)

[Paul Kirth via llvm-commits]

ilovepi wrote:

Didn't see: https://github.com/llvm/llvm-project/commit/898c116add170afb832d7f2f6bcfdc0daa6765f1, so I'm closing.

https://github.com/llvm/llvm-project/pull/99252