Also fix the run by setting up the environment in non-deprecated way.
Always run with --debug to understand better what sort of stuff is happening in
the background. Also split out the bmake bootstrap stage (takes about 31s on
ubuntu, but 1m14 on macOS?)
Drops the dependency on coreutils (realpath, nproc) and thus (?) fixes macOS to
be just as fast (4 logical cores vs 2 physical cores before, go figure.)
Reviewed by: arichardson
This builds the kernel-toolchain target and an amd64 GENERIC kernel on
Ubuntu 18.04, 20.04 and the latest macOS to ensure that new changes
don't regress building on non-FreeBSD hosts.
Reviewed By: emaste, lwhsu
Differential Revision: https://reviews.freebsd.org/D26512
