[clang] [clang] Add sincos builtin using `llvm.sincos` intrinsic (PR #114086)

[Simon Pilgrim via cfe-commits]

RKSimon wrote:

CC @rohitaggarwal007 who added sincos vectorisation for amdlibm recently - hopefully we can get ensure amdlibm uses the new builtin + intrinsic safely

https://github.com/llvm/llvm-project/pull/114086