Support of mips & mips64 for openmprtl

Summary:
Implemented by Dejan Latinovic
See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=790735 for more more information

Reviewers: AndreyChurbanov, jlpeyton

Subscribers: openmp-commits, mgorny

Differential Revision: https://reviews.llvm.org/D26576

llvm-svn: 289032