Do not specify the -B option when executing the sub-make. In the BSD

Do not specify the -B option when executing the sub-make.  In the BSD
make, -B is a compatibility option to execute shell commands one per line.
In GNU make (as of vers 3.80) -B is --always-make, which forces all targets
to be made regardless of whether they are out of date or not.

Since both GNU make and our make use MAKEFLAGS to pass build flags between
invocations, -B gets propogated down the chain into the gnu make and blows
everything to itsy bitsy little pieces.