[OPENMP, NVPTX] Do not globalize local variables in parallel regions.

[OPENMP, NVPTX] Do not globalize local variables in parallel regions.

In generic data-sharing mode we are allowed to not globalize local
variables that escape their declaration context iff they are declared
inside of the parallel region. We can do this because L2 parallel
regions are executed sequentially and, thus, we do not need to put
shared local variables in the global memory.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@336567 91177308-0d34-0410-b5e6-96231b3b80d8