[OpenMP][bugfix] Add missing math functions variants for log and abs.

Summary: When including the random header in C++, some of the math functions it relies on are not present in the CUDA headers. We include this variants in this case.

Reviewers: jdoerfert, hfinkel, tra, caomhin

Reviewed By: tra

Subscribers: efriedma, guansong, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D62046

llvm-svn: 361066