Changed declarations from Attr to InheritableAttr as they are already being processed that way semantically.

Patch thanks to Dean Sutherland!  Reviewed by Eli Friedman.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186598 91177308-0d34-0410-b5e6-96231b3b80d8
Separate the notion of 'context' when recursing down in the parser and actual errors.

Summary:
Change how error messages are constructed and stored in Diagnostics.
Separate the notion of 'context' when recursing down in the parser and actual errors.
This will simplify adding some new features, like argument overloading and error recovery.

Reviewers: klimek

CC: cfe-commits, revane

Differential Revision: http://llvm-reviews.chandlerc.com/D1168

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186602 91177308-0d34-0410-b5e6-96231b3b80d8