[analyzer] Add checker to verify the correct usage of the MPI API
This commit adds a static analysis checker to verify the correct usage of the MPI API in C
and C++. This version updates the reverted r271981 to fix a memory corruption found by the
Three path-sensitive checks are included:
- Double nonblocking: Double request usage by nonblocking calls without intermediate wait
- Missing wait: Nonblocking call without matching wait.
- Unmatched wait: Waiting for a request that was never used by a nonblocking call
Examples of how to use the checker can be found at https://github.com/0ax1/MPI-Checker
A patch by Alexander Droste!
Reviewers: zaks.anna, dcoughlin
Differential Revision: http://reviews.llvm.org/D21081