Fixed clib's GNUmakefile to build without mt19937ar.c.
Added clib to build target in GNUmakefile.
Moved cpplib build target to local in GNUmakefile.
Moved zlib build target to local in GNUmakefile.

Also added ignore patterns for generated outputs for zlib.
Moved Squirrel build target to local subdir for GNUmakefile.

A mkdir command is added to let a clean git checkout build the target
libraries.  We don't really need sq command line tool, but the default
Squirrel Makefile does not provide a way to avoid it's creation.
We may be permitted to modify the Makefile in the Squirrel source
according to squirrel3/COPYRIGHT, but I'm afraid doing so will make
future merge with library updates hard.