[OpenMP] Add support for close map modifier in Clang
This patch adds support for the close map modifier in Clang.
This ensures that the new map type is marked and passed to the OpenMP runtime appropriately.
Reviewers: ABataev, caomhin, jdoerfert, kkwli0
Reviewed By: ABataev
Subscribers: kkwli0, Hahnfeld, saghir, guansong, cfe-commits
Differential Revision: https://reviews.llvm.org/D65341