This patch implements an AST matching framework that allows to write

tools that match on the C++ ASTs. The main interface is in ASTMatchers.h,
an example implementation of a tool that removes redundant .c_str() calls
is in the example RemoveCStrCalls.cpp.

Various contributions:
Zhanyong Wan, Chandler Carruth, Marcin Kowalczyk, Wei Xu, James Dennett.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@132374 91177308-0d34-0410-b5e6-96231b3b80d8