Add clang-format-fuzzer target

Summary:
This adds clang-format-fuzzer binary,
which depends on the Fuzzer lib,
see http://reviews.llvm.org/D7184

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

llvm-svn: 227354