makedef.pl: Handle O flag

The O flags says to use 'perl_' instead of 'Perl_' if the p flag is not
also present.  This does that

Author: khwilliamson

makedef.pl

@@ -814,8 +814,12 @@ sub readvar {
 	    # mean "don't export"
 	    next if $seen{$func}++;
 	    # Should we also skip adding the Perl_ prefix if $flags =~ /o/ ?
-	    $func = "Perl_$func" if ($flags =~ /[psX]/ && $func !~ /^Perl_/);
+            my $prefix = ($flags =~ /[psX]/) ? 'Perl_'
+                       : ($flags =~ /O/) ? 'perl_'
+                       : "";
+	    $func = "$prefix$func" if $prefix && $func !~ /^$prefix/;
 	    ++$export{$func} unless exists $skip{$func};
+
 	}
     }
 }