[clang-tidy] Possibility of displaying duplicate warnings

Summary: In case a checker is registered multiple times as an alias, the emitted warnings are uniqued by the report message. However, it is random which checker name is included in the warning. When processing the output of clang-tidy this behavior caused some problems. In this commit the uniquing key contains the checker name too.

Reviewers: alexfh, xazax.hun, Szelethus, aaron.ballman, lebedev.ri, JonasToth, gribozavr

Reviewed By: alexfh

Subscribers: dkrupp, whisperity, rnkovacs, mgrang, cfe-commits

Patch by Tibor Brunner!

Tags: #clang

Differential Revision: https://reviews.llvm.org/D65065

llvm-svn: 369763