[OpenMP] Add support for multidimensional array sections in map clause SEMA.

Summary: In some cases it can be proved statically that multidimensional array section refer to contiguous storage and can therefore be allowed in a map clause. This patch adds support for those cases in SEMA.

Reviewers: hfinkel, carlo.bertolli, arpith-jacob, kkwli0, ABataev

Subscribers: cfe-commits, fraggamuffin, caomhin

Differential Revision: http://reviews.llvm.org/D17547

llvm-svn: 263019