teach makedef.pl an alternate macro for PERL_COPY_ON_WRITE

otherwise a -DPERL_NO_COW perl win32 build fails during linking perl523.dll
with missing Perl_sv_setsv_cow

Author: Daniel Dragan

makedef.pl

@@ -285,7 +285,7 @@ sub readvar {
 			 );
 }
 
-unless ($define{'PERL_COPY_ON_WRITE'}) {
+if (!$define{'PERL_COPY_ON_WRITE'} || $define{'PERL_NO_COW'}) {
     ++$skip{Perl_sv_setsv_cow};
 }