Fix Subdirectory Artifact Builds

Makefile

@@ -143,7 +143,9 @@ endef
 
 define add_target
         ifeq ($(.DEFAULT_GOAL),artifacts)
-                .DEFAULT_GOAL := $(1)
+                ifneq (,$(wildcard ./Makefile.conf))
+                        .DEFAULT_GOAL := $(1)
+                endif
         endif
 
         ifneq (,$$(findstring .a,$(1)))