Added -w to calls to xpidl. It's been in rules.mk for a while; I was shocked (shocked!) to find it wasn't here.

config/rules.mak

@@ -662,7 +662,7 @@ XPIDL_TYPELIBS=$(XPIDLSRCS:.idl=.xpt)
 XPIDL_TYPELIBS=$(XPIDL_TYPELIBS:.\=.\_xpidlgen\)
 
 .idl{$(XPIDL_GEN_DIR)}.xpt:
-        $(XPIDL_PROG) -m typelib $(XPIDL_INCLUDES) -o $* $<
+        $(XPIDL_PROG) -m typelib -w $(XPIDL_INCLUDES) -o $* $<
 
 !ifndef XPIDL_MODULE
 XPIDL_MODULE = $(MODULE)
@@ -682,7 +682,7 @@ $(XPIDL_GEN_DIR):
 	-mkdir $(XPIDL_GEN_DIR)
 
 .idl{$(XPIDL_GEN_DIR)}.h:
-        $(XPIDL_PROG) -m header $(XPIDL_INCLUDES) -o $* $<
+        $(XPIDL_PROG) -m header -w $(XPIDL_INCLUDES) -o $* $<
 
 
 $(DIST)\include: