make_ext.pl: Use version.pm for version cmp

make_ext.pl: Use version.pm for version cmp

We do a version comparison to determine whether Makefile.PL needs to
be run (in case a module version changed).  The simple string compar-
ison we have done up till now fails if the two version numbers differ
simply by a trailing zero (as currently happens with DB_File, which
is at version 1.840, with XS_VERSION set to 1.84.  Since version.pm’s
routines are compiled into miniperl, there is no reason not to do this
‘properly’, and it stops multiple ‘make’ invocations from rebuilding
DB_File again, and again....