[include-fixer] use includer of .inc header to be the file path of a symbol from .inc header.

Summary: added PathConfig.cpp and use includer of .inc header to be the file path of a symbol from .inc header.

Reviewers: bkramer

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D20855

llvm-svn: 271385