[OpenCL] Fix OpenCL and SPIR version metadata generation.

Summary: OpenCL and SPIR version metadata must be generated once per module instead of once per mangled global value.

Reviewers: Anastasia, yaxunl

Reviewed By: Anastasia

Subscribers: ahatanak, cfe-commits

Differential Revision: https://reviews.llvm.org/D34235

llvm-svn: 305796