[OpenMP] Adjust map type bits according to latest spec and use zero size array...

[OpenMP] Adjust map type bits according to latest spec and use zero size array sections for pointers.

Summary: This patch changes the bits used to specify the map types according to the latest version of the libomptarget document and add the support for zero size array section when pointers are being implicitly mapped. This completes the missing new 4.5 map semantics.

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

Subscribers: caomhin, cfe-commits

Differential Revision: http://reviews.llvm.org/D20111

llvm-svn: 270868