Fix building from within subdirs

Originally committed as revision 18881 to svn://svn.ffmpeg.org/ffmpeg/trunk

common.mak

@@ -71,7 +71,7 @@ EXAMPLES  := $(addprefix $(SUBDIR),$(addsuffix -example$(EXESUF),$(EXAMPLES)))
 OBJS      := $(addprefix $(SUBDIR),$(OBJS))
 TESTPROGS := $(addprefix $(SUBDIR),$(addsuffix -test$(EXESUF),$(TESTPROGS)))
 
-DEP_LIBS := $(foreach NAME,$(FFLIBS),lib$(NAME)/$($(BUILD_SHARED:yes=S)LIBNAME))
+DEP_LIBS := $(foreach NAME,$(FFLIBS),$(BUILD_ROOT_REL)/lib$(NAME)/$($(BUILD_SHARED:yes=S)LIBNAME))
 
 ALLHEADERS := $(subst $(SRC_DIR)/,$(SUBDIR),$(wildcard $(SRC_DIR)/*.h $(SRC_DIR)/$(ARCH)/*.h))
 checkheaders: $(filter-out %_template.ho,$(ALLHEADERS:.h=.ho))