Emit warning if define or undef reserved identifier or keyword.
Summary:
This change implements warnings if macro name is identical to a keyword or
reserved identifier. The warnings are different depending on the "danger"
of the operation. Defining macro that replaces a keyword is on by default.
Other cases produce warning that is off by default but can be turned on
using option -Wreserved-id-macro.
This change fixes PR11488.
Reviewers: rnk
Reviewed By: rnk
Subscribers: rnk, cfe-commits
Differential Revision: http://reviews.llvm.org/D6194
llvm-svn: 223114