Make tlb generation from idl files dependent on widl.

diff --git a/Make.rules.in b/Make.rules.in
index 230bd69..b8667e3 100644
--- a/Make.rules.in
+++ b/Make.rules.in
@@ -271,6 +271,8 @@
 
 $(IDL_SRCS:.idl=.h): $(WIDL)
 
+$(RC_TLB:.idl=.tlb): $(WIDL)
+
 $(SUBDIRS): dummy
 	@cd $@ && $(MAKE)