[libclc] [libclc] Add (fast) normalize to CLC; add half overloads (PR #139759)

[Matt Arsenault via cfe-commits]

arsenm wrote:

> I wasn't sure if this was necessary so this commit replaces the vector2 versions of the constants with the vector3/vector4 ones. The OpenCL-CTS seems okay with it. If this is incorrect then it's not very difficult to split them back out again.

Does it pass with -cl-denorms-are-zero? 


https://github.com/llvm/llvm-project/pull/139759