Minor code cleanup of Klocwork issues

Minor code cleanup of Klocwork issues. Fatal messages are given no return
attribute. Define and use KMP_NORETURN to work for multiple C++ versions.

Patch by Terry Wilmarth

Differential Revision: https://reviews.llvm.org/D37275


git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@312538 91177308-0d34-0410-b5e6-96231b3b80d8