[OPENMP][Analysis] Add analysis of the map clauses.

Summary:
Added basic analysis of map clauses. Only map clauses with to and tofrom
map type must be analyzed since all other map types (alloc, delete, etc.) do not require to use the value of the initial variable, instead they create the new copy of the variable.

Reviewers: NoQ

Subscribers: guansong, cfe-commits, kkwli0, caomhin

Tags: #clang

Differential Revision: https://reviews.llvm.org/D66668

llvm-svn: 370214