[clang] [llvm] [clang] Reland Add tanf16 builtin and support for tan constrained intrinsic (PR #94559)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

Can we change the target-independent bits of the tan() implementation in the backend so it doesn't require each target to explicitly request that tan() needs to be expanded?  It should be possible to adjust the code in TargetLoweringBase.cpp a bit so FTAN defaults to being expanded for all types.

https://github.com/llvm/llvm-project/pull/94559