[include-fixer] Add a find-all-symbols tool for include-fixer.

Summary:
The find-all-symbols tool generates a yaml symbol database for
include-fixer.

The symbol matcher is originally written by Xiaoyi Liu.

Reviewers: bkramer, djasper

Subscribers: cfe-commits, klimek, ioeric

Differential Revision: http://reviews.llvm.org/D19482

llvm-svn: 267719