[libc] [llvm] [libc][math][c23] Add rsqrtf() function (PR #159615)

[Anton Shepelev via llvm-commits]

amemov wrote:

@lntue, I think it is now ready to be merged unless @overmighty might have some other comments.

I initially misread the comment about Bazel that he left. After re-reading it one more time today I realized that, and pushed the changes that address it. Now rsqrtf and rsqrtf16, have correct dependencies that correspond to their current states. 

https://github.com/llvm/llvm-project/pull/159615