[OPENMP] parsing and sema support for 'close' map-type-modifier

[OPENMP] parsing and sema support for 'close' map-type-modifier

A map clause with the close map-type-modifier is a hint to
prefer that the variables are mapped using a copy into faster
memory.

Patch by Ahsan Saghir (saghir)

Differential Revision: https://reviews.llvm.org/D55719

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@349551 91177308-0d34-0410-b5e6-96231b3b80d8