Revert "build: Add DEP_LIBS dependency directly to the shared library build rule."

This reverts commit 729f953f.

subdir.mak

@@ -39,11 +39,15 @@ $(SUBDIR)%$(EXESUF): $(SUBDIR)%.o
 $(SUBDIR)$(SLIBNAME): $(SUBDIR)$(SLIBNAME_WITH_MAJOR)
 	$(Q)cd ./$(SUBDIR) && $(LN_S) $(SLIBNAME_WITH_MAJOR) $(SLIBNAME)
 
-$(SUBDIR)$(SLIBNAME_WITH_MAJOR): $(OBJS) $(SUBDIR)lib$(NAME).ver $(DEP_LIBS)
+$(SUBDIR)$(SLIBNAME_WITH_MAJOR): $(OBJS) $(SUBDIR)lib$(NAME).ver
 	$(SLIB_CREATE_DEF_CMD)
 	$$(LD) $(SHFLAGS) $(FFLDFLAGS) -o $$@ $$(filter %.o,$$^) $(FFEXTRALIBS) $(EXTRAOBJS)
 	$(SLIB_EXTRA_CMD)
 
+ifdef SUBDIR
+$(SUBDIR)$(SLIBNAME_WITH_MAJOR): $(DEP_LIBS)
+endif
+
 clean::
 	$(RM) $(addprefix $(SUBDIR),*-example$(EXESUF) *-test$(EXESUF) $(CLEANFILES) $(CLEANSUFFIXES) $(LIBSUFFIXES)) \
 	    $(foreach dir,$(DIRS),$(CLEANSUFFIXES:%=$(SUBDIR)$(dir)/%)) \