[clang] [Clang] fix crash parsing forbidden attribute args in pragma attributes (PR #182362)

[Oliver Hunt via cfe-commits]

https://github.com/ojhunt requested changes to this pull request.

This is a correct fix for this particular case, as it results in correct fixit.

But the actual bug is in the err_cxx11_attribute_forbids_arguments diagnostic in `ParseCXX11AttributeArgs` as the endloc parameters is intended as an optional parameter, so it should only be emitting the fixit if the endloc is available.

Could you also fix that as part of this PR?

https://github.com/llvm/llvm-project/pull/182362