[libclc] [libclc] Set OpenCL C version for each target (PR #135733)

[Wenju He via cfe-commits]

wenju-he wrote:

> > LGTM. That means we compile for the last OpenCL version, which is 3.0, and enable all OpenCL extensions/features, right?
> 
> Yes. Otherwise you have to still write the code to work with the lowest common denominator.

done in commit https://github.com/llvm/llvm-project/pull/135733/commits/b3653cdcfde00ece9ac929d6c0555c237e87ff86

https://github.com/llvm/llvm-project/pull/135733