[libclc] [libclc] Move conversion builtins to the CLC library (PR #124727)

[Romaric Jodin via cfe-commits]

rjodinchr wrote:

This is not correct for `clspv`. It breaks everything and it feels like it needs quite some work to fix. FYI, I'll be OOO from Feb 3 to Feb 21. Can it wait that long? I'm not sure I'll have enough time to figure it out before the end of the week.

https://github.com/llvm/llvm-project/pull/124727