[clang-tidy] openmp-use-default-none - a new check

Summary:
Finds OpenMP directives that are allowed to contain `default` clause,
but either don't specify it, or the clause is specified but with the kind
other than `none`, and suggests to use `default(none)` clause.

Using `default(none)` clause changes the default variable visibility from
being implicitly determined, and thus forces developer to be explicit about the
desired data scoping for each variable.

Reviewers: JonasToth, aaron.ballman, xazax.hun, hokein, gribozavr

Reviewed By: JonasToth, aaron.ballman

Subscribers: jdoerfert, openmp-commits, klimek, sbenza, arphaman, Eugene.Zelenko, ABataev, mgorny, rnkovacs, guansong, cfe-commits

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

Differential Revision: https://reviews.llvm.org/D57113

llvm-svn: 356801