Use generational_gc. It's not good to get rid of the 4-% speedup

Configure.pl

@@ -26,7 +26,7 @@
         my $prefix  = $options{'gen-parrot-prefix'} || cwd()."/parrot_install";
         # parrot's Configure.pl mishandles win32 backslashes in --prefix
         $prefix =~ s{\\}{/}g;
-        my @command = ($^X, "build/gen_parrot.pl", "--prefix=$prefix", ($^O !~ /win32/i ? "--optimize" : ()), @opts);
+        my @command = ($^X, "build/gen_parrot.pl", "--prefix=$prefix", ($^O !~ /win32/i ? "--optimize --gc=gms" : ()), @opts);
 
         print "Generating Parrot ...\n";
         print "@command\n\n";