[OpenMP] Fix SEMA bug in the capture of global variables in template functions.

Summary:
Target regions require globals to be captured. This patch fixes a bug exposed when that happens in a template function.


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

Subscribers: guansong, ABataev, cfe-commits, caomhin, fraggamuffin

Differential Revision: http://reviews.llvm.org/D18110

llvm-svn: 271001