Exit with a non-zero value in case any of the underlying clang-tidy
invocations exit with a non-zero value.
This is useful in case WarningsAsErrors is enabled for some of the
checks: if any of those checks find something, the exit status now
reflects that.
Also add the ability to use run-clang-tidy.py via lit, and assert that
the exit code is not 0 when modernize-use-auto is triggered
intentionally.
Reviewers: alexfh, aaron.ballman
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D44366
llvm-svn: 327854
Roman Lebedev