openwcom.mak: use %null instead of @Rem for $(SIDE)

%null appears to be the recommended way to do $(SIDE) on WMAKE.

Suggested-by: KO Mying-Hun <komh78@gmail.com>
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>

Author: H. Peter Anvin

Mkfiles/openwcom.mak

@@ -34,7 +34,7 @@ RUNPERL         = $(PERL) $(PERLFLAGS)
 RM_F		= -del /f
 LN_S		= copy
 EMPTY		= copy nul:
-SIDE		= @rem Created by side effect
+SIDE		= %null Created by side effect
 
 MAKENSIS        = makensis