[clang-tidy] MPITypeMismatchCheck

This check verifies if buffer type and MPI (Message Passing Interface)
datatype pairs match. All MPI datatypes defined by the MPI standard (3.1)
are verified by this check. User defined typedefs, custom MPI datatypes and
null pointer constants are skipped, in the course of verification.

Instructions on how to apply the check can be found at:
https://github.com/0ax1/MPI-Checker/tree/master/examples

Patch by Alexander Droste!

Differential revision: https://reviews.llvm.org/D21962

llvm-svn: 277516