The "Reject builds with pymake" patch from bug 1027890 seems to have broken building with comm-central. My guess is that the usage of topsrcdir is wrong in this case. The error one gets is: "Exception: Could not find a suitable make implementation." on Mac (or the corresponding message about using mozmake for Windows). I don't think I have the knowledge to fix this, but if someone points me in the right direction I can give it a try!
Just to be explicit, I tested backing out rev 8aac3c8dc7bb from my copy of mozilla-central and I was able to run configure again. (And luckily it backs out cleanly.)
Created attachment 8447012 [details] [diff] [review] fixBuild.patch With this patch I can build again with mach. This is a simple copy-n-paste, I don't know what I'm doing here. Apologies for unneeded changes.
Richard's patch *does* get Mach builds going again for me. I do have problems on a 'recurse to Libs' towards the end of the build however. Building with mozmake directly bypasses that problem, which seems to be specific to my build envir. (Win7, vc11 with the win8 sdk.)