[SYCL] Start to move attribute handling to SemaSYCL

[frasercrmck]

This better reflects how Sema is organized upstream, following recent restructuring. Doing all of it at once (moving all SYCL-related code out of SemaDeclAttr) results in an unwieldy diff, interleaving additions and deletions in an unreadable way. Thus the patch is split up into parts for better reviewability.

Code has been moved to a new cpp file - SemaSYCLAttrDecl.cpp - as SemaSYCL.cpp is already large.

[elizabethandrews]

Thanks for doing this. I believe @premanandrao was/is also taking a look at this. He is OOO till Monday. So if you are alright with waiting for this patch to be merged, I would like him to comment as well.

[smanna12]

LGTM. Thank you for the improvements.

[frasercrmck]

Thanks for doing this. I believe @premanandrao was/is also taking a look at this. He is OOO till Monday. So if you are alright with waiting for this patch to be merged, I would like him to comment as well.

ping, @premanandrao - thanks!

[premanandrao]

Thanks for doing this. I believe @premanandrao was/is also taking a look at this. He is OOO till Monday. So if you are alright with waiting for this patch to be merged, I would like him to comment as well.

ping, @premanandrao - thanks!

Thanks for the ping. @elizabethandrews also pinged me on this change. Thanks!

I like the changes and the split to the new file.

[premanandrao]

Please resolve the conflicts, but LGTM.

[frasercrmck]

Please resolve the conflicts, but LGTM.

Thanks for the review. Yeah I fixed conflicts yesterday and it's already conflicting again. It will be good to flush this PR.

[frasercrmck]

@intel/llvm-gatekeepers this is good to merge, thank you!