Makefile: fix dependency includes

Makefile

@@ -1,13 +1,13 @@
 # Executable
 TARGET := main.out
 
-# Paths to source, dependency, object files
+# Paths to source, include, dependency, and object files
 SPATH = src
 IPATH = inc
 DPATH = dep
 OPATH = obj
 
-VPATH = $(SPATH) $(OPATH) $(IPATH) $(DPATH)
+VPATH = $(SPATH) $(IPATH) $(DPATH) $(OPATH)
 
 # compiler and compiler flags
 CC = g++
@@ -38,11 +38,11 @@ $(DPATH) $(OPATH):
 %.out: $(OBJECTS)
 	$(CC) $(CFLAGS) -o $@ $^
 # Make the object and dependency files
-$(OPATH)/%.o $(DPATH)/%.d: $(SPATH)/%.cpp
+$(OPATH)/%.o: $(SPATH)/%.cpp
 	$(CC) $(CFLAGS) -MF $(DPATH)/$(@F:.o=.d) -o $@ -c $<
 
-# Don't delete object files:
-.PRECIOUS: $(OPATH)/%.o $(DPATH)/%.d
+# Don't autodelete object files:
+.SECONDARY: $(OPATH)/%.o
 
 # use dependencies when rebuilding
--include $(addprefix $(DPATH)/,$(wildcard *.d))
+-include $(wildcard $(DPATH)/*.d)