Enhance debug info namespace test to check for context/scope reference

The differing file (due to the #line directive in the original source) is for
future testing improvements coming soon.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177560 91177308-0d34-0410-b5e6-96231b3b80d8
Refactor file/directory path in namespace debug info to refer directly to the pair rather than the DIFile

(paired to a Clang test - excuse the buildbot skew/fallout)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177566 91177308-0d34-0410-b5e6-96231b3b80d8