[libc-commits] [libc] [libc][stdfix] Implement mulifx functions (PR #235602)

[Jaeyong Lee via libc-commits]

npmania wrote:

https://github.com/llvm/llvm-project/pull/235602/commits/e790eab24845c1691568836bd06b8470c538686b, https://github.com/llvm/llvm-project/pull/235602/commits/783c9e8098f38897f0d87bb9a58947a1a053fc07 apply to `divifx` as well. I left that for a separate NFC.

https://github.com/llvm/llvm-project/pull/235602