common.mak: add forgotten hunk from last merge

Found-by: jamal <jamrial@gmail.com>
Author of the hunk: Mans Rullgard <mans@mansr.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

common.mak

@@ -56,8 +56,8 @@ COMPILE_S = $(call COMPILE,AS)
 %.o: %.S
 	$(COMPILE_S)
 
-%.ho: %.h
-	$(CC) $(CCFLAGS) -c $(CC_O) -x c $<
+%.h.c:
+	$(Q)echo '#include "$*.h"' >$@
 
 %.ver: %.v
 	$(Q)sed 's/$$MAJOR/$($(basename $(@F))_VERSION_MAJOR)/' $^ > $@