void rather than empty parameter for Perl___notused.

void rather than empty parameter for Perl___notused.

Without this, the VMS compiler, with warnings cranked up to level 4,
emits pages and pages of things like:

    dVAR;
....^
%CC-I-NOPARMLIST, The declaration of the function Perl___notused has
an empty parameter list.  If the function has parameters, they should
be declared here; if it has no parameters, "void" should be specified
in the parameter list.
at line number 100 in file MDA0:[SMOKE.blead]perl.c;1

Over 2,000 of these plus other warnings yields a smoke report of 750K,
which is quite a bit over the 400K limit of the perl.org mailing lists,
not to mention being a slow read.