Add clang-format-fuzzer target
This adds clang-format-fuzzer binary,
which depends on the Fuzzer lib,
This fuzer has found ~15 bugs so far, and I hope to set up a bot for it.
Test Plan: run on a bot.
Reviewers: samsonov, djasper
Reviewed By: djasper
Subscribers: curdeius, cfe-commits
Differential Revision: http://reviews.llvm.org/D7202