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

[Fraser Cormack via cfe-commits]

frasercrmck wrote:

> LGTM. That means we compile for the last OpenCL version, which is 3.0, and enable all OpenCL extensions/features, right? libclc is implemented using functions supported by clang, so it is unlikely a target has libclc build error in generic libclc files that are shared for all targets. When libclc is linked to application module, libclc built-ins implementation of unsupported extensions/features won't be linked in because these built-ins won't exist in the user module. If the application code uses an unsupported extension, frontend would report error already. There could be problem if application modules links in a supported libclc built-in function which calls another libclc built-in that belongs to unsupported special extension/feature, but I think this scenario is unlikely and the supported built-in should be fixed to not using unsupported feature. @frasercrmck What do you think?

Sounds good to me. I hope that by having the internal CLC library we can largely avoid the last scenario, as CLC should be less dependent on the OpenCL C version. An OpenCL 1.2 module could still call a builtin that makes internal use of CLC `ctz`, for example.

Anyway, sorry for complicating the PR with my suggestion. I was being unnecessarily conservative.

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