Removing a FIXME from the attribute parsing code by now passing along the scope and...

Removing a FIXME from the attribute parsing code by now passing along the scope and syntax information for attributes with custom parsing. It turns out not to matter too much because the FIXME wasn't quite true -- none of these attributes have a C++11 spelling. However, it's still a good change (for instance, we may add an attribute with a type arg in the future for which this code now behaves properly).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@213191 91177308-0d34-0410-b5e6-96231b3b80d8