Makefile: make -MF write to .d file instead of stdout

This way, the default rule for .c.o can be used, simplifying the
Makefile a bit more.

Makefile

@@ -4,7 +4,7 @@
 PROJECT = slcl
 O = -Og
 CDEFS = -D_FILE_OFFSET_BITS=64 # Required for large file support on 32-bit.
-CFLAGS = $(O) $(CDEFS) -g -Wall -Idynstr/include -MD -MF -
+CFLAGS = $(O) $(CDEFS) -g -Wall -Idynstr/include -MD -MF $(@:.o=.d)
 LIBS = -lcjson -lssl -lm -lcrypto
 LDFLAGS = $(LIBS)
 DEPS = $(OBJECTS:.o=.d)
@@ -30,7 +30,4 @@ clean:
 $(PROJECT): $(OBJECTS)
 	$(CC) $(OBJECTS) $(LDFLAGS) -o $@
 
-.c.o:
-	$(CC) $(CFLAGS) -c $< -o $@ > $(@:.o=.d)
-
 -include $(DEPS)