use /bin/sh instead of /bin/bash (which is not available on all UNIX systems)

also, use cc instead of gcc (no need to compile HOL4 with gcc)

Make the organsiation of the mllex source-code a bit cleaner so that
the polyml version can be built more easily. If you have polyml
installed nicely, it should be possible to get a poly version of mllex
by just going
make -f Holmakefile mllex.exe
in the tools/mllex directory. The tricksiness in Holmakefile is more
cute than useful, as it's not used by Holmake.

A MoscowML compilable version of the "standard" mllex tool, as used by
both SML/NJ and MLton. The source code is also compilable by mlton,
though this is cute more than useful as mlton comes with a version of mllex
anyway.