[libc-commits] [compiler-rt] [libc] [llvm] [Compiler-rt][builtins] introduce libc math routines (PR #197950)

[via libc-commits]

https://github.com/lntue requested changes to this pull request.

This PR is for demonstrating the integration.  Once everything looks ok, we will need to split it into 3 PRs in the following order:
- [libc] Add addtf3.h and builtins.h to shared headers (+ smoke tests)
- [compiler-rt] Add compiler-rt cmake option to build compiler builtins with LLVM libc
- [CI] Add precommit CIs to test compiler-rt + LLVM libc integration.

@compnerd @statham-arm 

https://github.com/llvm/llvm-project/pull/197950