[libc] [llvm] [libc][math] Add tgammabf16 math support for bfloat16. (PR #208689)

[via llvm-commits]

https://github.com/Sukumarsawant approved this pull request.

cc: @lntue for the math part confirmation
Though I still have some doubts about double being used, but since you confirmed, LGTM apart from a small addition .

https://github.com/llvm/llvm-project/pull/208689