[DEBUGINFO, NVPTX]Emit last debugging directives.

[DEBUGINFO, NVPTX]Emit last debugging directives.

Summary:
We may end up with not emitted debug directives at the end of the module
emission. Patch fixes this problem emitting those last directives the
end of the module emission.

Reviewers: echristo

Subscribers: jholewinski, llvm-commits

Differential Revision: https://reviews.llvm.org/D54320

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@348495 91177308-0d34-0410-b5e6-96231b3b80d8