Introduce bsd.autotools.mk to the world, ripped from bsd.port.mk
This is essentially a null-commit, with the one exception that
the "patch-libtool" target is now called "patch-autotools" for
consistency with "run-autotools".
Many thanks to kris for testing on the 4-exp bento cluster
Approved by: portmgr (kris)
Verified by: bento 4-exp