[OPENMP] Deal with additional store inserted by Clang under -fno-PIC for PowerPC.

Changing the default from -fPIC to -fno-PIC on PowerPC exposed an issue in
OpenMP for PowerPC.
The issue is reported here:
https://bugs.llvm.org/show_bug.cgi?id=40082

This is a fix for that issue.
Also removed the XFAIL from the two tests that were failing under -fno-PIC.

Differential Revision: https://reviews.llvm.org/D56286

llvm-svn: 355229