configure: remove duplicated CFLAGS from DEPFLAGS

The DEPFLAGS definition included the CFLAGS variable. All uses of
DEPFLAGS in Makefile use CFLAGS too, so this resulted in duplicated
options. Make DEPFLAGS contain "-MD -MP" only.

configure

@@ -2459,7 +2459,7 @@ else
 fi
 
 cflag_check -mno-omit-leaf-frame-pointer && cflags_no_omit_leaf_frame_pointer="-mno-omit-leaf-frame-pointer"
-cflag_check -MD -MP && DEPFLAGS="-MD -MP $CFLAGS"
+cflag_check -MD -MP && DEPFLAGS="-MD -MP"
 
 
 if test -n "$LDFLAGS" ; then