bug 2450: Allow build of RELEASE 3.2 from master's bmake

bug 2450: Allow build of RELEASE 3.2 from master's bmake

It was not possible to build RELEASE 3.2 once the world was updated to
the 3.3 development branch.  The makefiles were incompatible with bmake.
It was possible to build RELEASE 3.2 with only a change to bsd.cpu.mk,
but parallel builds still failed.  The remaining changes and the previous
cherry-pick were all done to support parallel builds when building this
release branch from a system equipped with bmake as the system make.

<https://bugs.dragonflybsd.org/issues/2450>