[OPENMP, NVPTX] Improve globalization of the variables captured by value.

[OPENMP, NVPTX] Improve globalization of the variables captured by value.

If the variable is captured by value and the corresponding parameter in
the outlined function escapes its declaration context, this parameter
must be globalized. To globalize it we need to get the address of the
original parameter, load the value, store it to the global address and
use this global address instead of the original.

Patch improves globalization for parallel|teams regions + functions in
declare target regions.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@327654 91177308-0d34-0410-b5e6-96231b3b80d8