[clang] Implement the `fmod` intrinsic (PR #130320)

[Farzon Lotfi via cfe-commits]

farzonl wrote:

@kmpeng  could you rebase  and squash these commits. If I try and squash merge its going to set your personal email as the author  because your first commit was using your personal: https://github.com/llvm/llvm-project/commit/ef16da4479d9d2034f3b6072410b488d7568ce88.patch

but looks like you switch to your work email later: https://github.com/llvm/llvm-project/commit/bd1a02b0e7bacf1ecbc54de8356aef0a5df8bd5d.patch

The only way I know how to fix this is if the first commit was using your work email hence my ask to rebase and squash to one commit.

https://github.com/llvm/llvm-project/pull/130320