The Clang side of the debugger "target" patches. Slightly repurpose -ggdb and
add -glldb and -gsce to set GDB, LLDB, or PS4 as the "debugger target."
This is thematically consistent with GCC options such as -ggdb and -gvms.
No Clang functionality depends on this yet, although conditionally importing
anonymous namespaces (in review) could use this instead of a triple test.
The LLVM part is available at http://reviews.llvm.org/D8506
I'll whip up the obvious -### driver test but thought I'd put this out now.