[ASTMatchers] Add clang-query support for equals matcher

Summary:
This allows the clang-query tool to use matchers like
"integerLiteral(equals(32))". For this to work, an overloaded function
is added for each possible parameter type.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D33094

llvm-svn: 305022