Cleanup of ASTMatcher macros and adding support for overloaded matchers.

Cleanup of ASTMatcher macros and adding support for overloaded matchers.

This is in preparation for adding other overloaded matchers. This change
alone is a net win in LOC.
I went through all matchers and looked whether we could now encode them
as macro, or simplify them with the matcher atoms that were not
available before.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174540 91177308-0d34-0410-b5e6-96231b3b80d8