Using +build useflag (I'm trying to prepare an experimental stage for G/FBSD), make unconditionally uses make as name for the binary. This overwrites BSD's make and bails out everything from freebsd itself. The solution is to use the attached patch which names make "gmake" on non-GNU userlands. Not sure how Darwin should handle this, so I added osx@gentoo.org to CC for comments. Thanks, Diego
Created attachment 61136 [details, diff] make-build.patch
now in portage