lazy evaluation semantics, not the "assign it now" semantics. This
allows variables used in the program's CPPFLAGS to get the correct
values of e.g. MACHINE, MACHINE_ARCH, MACHINE_CPU, etc.
Problem was notices when propagating MACHINE and MACHINE_ARCH via
MAKEFLAGS (i.e. from the command line, rather than the environment).
For this to work, make sure you <bsd.hostprog.mk> is at least rev 1.15.
