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

[Wenju He via cfe-commits]

wenju-he wrote:

> I'd expect the libclc build (or any other runtime support library) to consistently use the same language version independent of the target. If the target doesn't support that version (which IIRC isn't actually a hard error anywhere) and fails to compile on some feature, those should be carved out into separate version dependent build (as in, this isn't a compile target property but a specific build target property)

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.
@frasercrmck What do you think?

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