DwarfDebug: Avoid creating new DebugLocs in the backend

Don't use `DebugLoc::getFnDebugLoc()`, which creates new `MDLocation`s,
in the backend.  We just want to grab the subprogram here anyway.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233601 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed