[libc] [llvm] [libc] use constexpr for sinpif (PR #176580)

[via llvm-commits]

DannyDaoBoYang wrote:

The Bazel problems are caused by recent changes in llvm/tools/llvm-ir2vec. I'll try to fix it here and move it to a separate pr. 

https://github.com/llvm/llvm-project/pull/176580