Makefile improvements.

Makefile improvements.

* Makefile.in (lib): Depend on am--refresh, to avoid a race.
(src): Remove duplicate dependency on FRC.
Invoke just one submake, not two.  Avoid the need for 'pwd'.
* lwlib/Makefile.in (all): Put this first.  Don't use double-colon
rules, as they are not portable according to POSIX.  Mark as phony.
* oldXMenu/Makefile.in (all, tags): Don't use double-colon rules, as they
are not portable according to POSIX.  Mark as phony.
* src/Makefile.in (config.status): Don't use double-colon rules, as
they are not portable according to POSIX.  Fix shell typo with `;
I guess this rule has never been tested?
(VCSWITNESS): New macro, to override any environment var.