ExternalProject: Use of cygwin's make tool in non-cygwin builds

@brad.king I’m trying to understand the rationale behind this quite old commit which handles the use of $(MAKE) in an ExternalProject step command. It seems to be invoking cygpath for a non-cygwin build and is forcing the use of cygwin’s make tool if it can be found. This seems odd given that we are not using cygwin for the build. Why favour cygwin over, say, msys make? What scenario are we trying to account for with that commit?

Back before ninja we had for a while attempted to parallize makefile builds on Windows by using a GNU make built on Cygwin but with a patch to handle Windows-style paths. We had a nightly build doing that for a while, and this patch was needed to make ExternalProject work on it. I expect it is okay to remove that code now.

That’s fantastic, it was going to complicate things for my refactored ExternalProject work. Now I can clean that up and should have that work ready for review once the current ExternalProject MR is merged. I’ll add a comment about this to the new MR when I put it up.