[OPENMP50]Initial support for use_device_addr clause.

Summary:
Added parsing/sema analysis/serialization support for use_device_addr
clauses.

Reviewers: jdoerfert

Subscribers: yaxunl, guansong, arphaman, sstefan1, llvm-commits, cfe-commits, caomhin

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D80404