Remove $FreeBSD$: one-line bare tag

Remove /^\s*\$FreeBSD\$$\n/

Move old fmake tests into bmake and hook them to the build.

This first step is mostly to prevent the code from rotting even further
and to ensure these do not get wiped when fmake's code is removed from
the tree.

These tests are currently being skipped because they detect the underlying
make is not fmake and thus disable themselves -- and the reason is that
some of the tests fail, possibly due to legitimate bugs. Enabling them to
run against bmake will come separately.

Lastly, it would be ideal if these tests were fed upstream but they are
not ready for that yet. In the interim, just put them under usr.bin/bmake/
while we sort things out. The existence of a different unit-tests directory
within here makes me feel less guilty about this.

Change confirmed working with a clean amd64 build.