[OpenMP][libomptarget] Fix data sharing and globalization infrastructure to work in SPMD mode

Summary: This patch fixes the data sharing infrastructure to work for the SPMD and non-SPMD cases.

Reviewers: ABataev, grokos, carlo.bertolli, caomhin

Reviewed By: ABataev, grokos

Subscribers: guansong, openmp-commits

Differential Revision: https://reviews.llvm.org/D49204

llvm-svn: 337013