[libclc] [libclc] Move fmin/fmax to the CLC library (PR #128506)

[Matt Arsenault via cfe-commits]

arsenm wrote:

These should use the regular builtin fmin / fmax. 

> I note that the comments around the use of canonicalize mention sNAN, which isn't required by the spec.

The spec is quite badly written on what's expected of snans here, and the conformance test doesn't test what is written in the spec (hoping to fix that [here](https://github.com/KhronosGroup/OpenCL-CTS/pull/2285)

https://github.com/llvm/llvm-project/pull/128506