[clang-tidy] Do not list enabled checks when -quiet is given to run-clang-tidy.

Summary: When run-clang-tidy is given the -quiet flag, do not output the potentially hundreds of enabled check names at the beginning.

Patch by svenpanne.

Reviewers: alexfh, JonasToth

Reviewed By: JonasToth

Subscribers: JonasToth, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D61849

llvm-svn: 360869