Add Makefile for creating the bh-executable and blackhole.o1-module
from the sources. Linking to libgambcgsc.so should also be supported now
if libgambcgsc.a doesn't exists.

The blackhole.o1 module can be used to open blackhole-interpreter session
without bh-executable.
e.g. gsc -i -e '(load "blackhole")' -