For example, on FreeBSD, bmake is the default make implementation. Thus, to
build CBQN, we must use 'gmake' invocations. This patch fixes the hardcoded call
to 'make' in build/build.
hasn't been bumped since •file.RealPath was added, which Singeli currently conditionally uses (and thus won't in older for_build-s); now •file.RealPath will be guaranteed to exist at build-time