[OpenMP][OMPT] Fix locking testcases for 32 bit architectures

https://reviews.llvm.org/D58454 did not fix the problem for a typical use
case of building LLVM with gcc or icc and then testing with the newly built
clang compiler.
The compilers do not agree on how to extend a 32-bit pointer to uint64, so
make the pointer unsigned first, before adjusting the size.

Patch by Joachim Protze

Differential Revision: https://reviews.llvm.org/D58506

llvm-svn: 361158