[OPENMP, NVPTX] Globalization of the private redeclarations.

[OPENMP, NVPTX] Globalization of the private redeclarations.

If the generic codegen is enabled and private copy of the original
variable escapes the declaration context, this private copy should be
globalized just like it was the original variable.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@327985 91177308-0d34-0410-b5e6-96231b3b80d8