[OPENMP][NVPTX]Fixed/improved support for globalization in team contexts.

[OPENMP][NVPTX]Fixed/improved support for globalization in team contexts.

Summary:
Current globalization scheme works correctly only for SPMD+lightweight
runtime mode and does not work for full runtime. Patch improves support
for the globalization scheme + reduces global memory consumption in
  lightweight runtime mode.
Patch adds runtime functions to work with the statically allocated
global memory. It allows to improve performance and memory consumption.
This global memory must be allocated by the compiler.

Reviewers: grokos, kkwli0, gtbercea, caomhin

Subscribers: guansong, jfb, openmp-commits

Differential Revision: https://reviews.llvm.org/D53943

llvm-svn: 345976