[PATCH] Add new debug kind LocTrackingOnly.

[David Blaikie]

Probably worth wiring up the command line support in the same patch &
including test coverage.

I'd probably start with the LLVM change (using a local Clang change to
generate IR, or just hand-hacking the removal of the llvm.dbg.cu node
in an IR sample) to make sure this strategy is plausible and that just
dropping the llvm.dbg.cu node is all that's required from the
front-end.

Have you tested this through LLVM? How's it look?

http://reviews.llvm.org/D4234