[libclc] libclc: increase fp16 support (PR #98149)

[Romaric Jodin via cfe-commits]

rjodinchr wrote:

Also, just leave that thought here: A next step might be to use `native` functions instead (when available). They should provide enough precision for half, but be more performance. Also as the accuracy is undefined for those functions, maybe it should be an opt-in option in the libclc (clspv would enable it for sure).

https://github.com/llvm/llvm-project/pull/98149