Summary: This patch implements the code generation for the `target update` directive. The implemntation relies on the logic already in place for target data standalone directives, i.e. target enter/exit data.
Reviewers: hfinkel, carlo.bertolli, arpith-jacob, kkwli0, ABataev
Subscribers: caomhin, cfe-commits
Differential Revision: http://reviews.llvm.org/D20650
llvm-svn: 270886
