[clang-tidy] openmp-exception-escape - a new check

[clang-tidy] openmp-exception-escape - a new check

Summary:
Finally, we are here!

Analyzes OpenMP Structured Blocks and checks that no exception escapes
out of the Structured Block it was thrown in.

As per the OpenMP specification, structured block is an executable statement,
possibly compound, with a single entry at the top and a single exit at the
bottom. Which means, ``throw`` may not be used to to 'exit' out of the
structured block. If an exception is not caught in the same structured block
it was thrown in, the behaviour is undefined / implementation defined,
the program will likely terminate.

Reviewers: JonasToth, aaron.ballman, baloghadamsoftware, gribozavr

Reviewed By: aaron.ballman, gribozavr

Subscribers: mgorny, xazax.hun, rnkovacs, guansong, jdoerfert, cfe-commits, ABataev

Tags: #clang-tools-extra, #openmp, #clang

Differential Revision: https://reviews.llvm.org/D59466

llvm-svn: 356802