build: do not add CFLAGS-yes to CFLAGS

CFLAGS-yes is never set so this serves no purpose.
Signed-off-by: Mans Rullgard <mans@mansr.com>

common.mak

@@ -73,7 +73,6 @@ endif
 
 OBJS-$(HAVE_MMX) +=  $(MMX-OBJS-yes)
 
-CFLAGS    += $(CFLAGS-yes)
 OBJS      += $(OBJS-yes)
 FFLIBS    := $(FFLIBS-yes) $(FFLIBS)
 TESTPROGS += $(TESTPROGS-yes)