Bug 1072778 (part 1) - Make |mach dmd| work on Linux. r=erahm.

--HG--
extra : rebase_source : 72b0f570dfacc694fc00fd2ec571c57747c8fe38
Bug 1072778 (part 2) - Use '-' instead of '_' in |mach dmd| flags. r=erahm.
DONTBUILD because |mach dmd| is NPOTB.