Don't use implicit rules for Makefile

This remove implicit rules + implicit variables.
Explicit rules like the generation of %.h and %.c from %.hx still works
as expected.

As an added bonus, now the output of make -d is readable.

As another added bonus, time spend on Makefiles is way smaller.
We run make -j3 in a fully compiled tree, and results are:

Before:

$ time make -j3
real 0m1.225s
user 0m1.660s
sys 0m0.253s

After:
$ time make -j3
real 0m0.422s
user 0m0.393s
sys 0m0.248s

Signed-off-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

rules.mak

@@ -1,4 +1,16 @@
 
+# Don't use implicit rules or variables
+# we have explicit rules for everything
+MAKEFLAGS += -rR
+
+# Files with this suffixes are final, don't try to generate them
+# using implicit rules
+%.d:
+%.h:
+%.c:
+%.m:
+%.mak:
+
 %.o: %.c
 	$(call quiet-command,$(CC) $(QEMU_CFLAGS) $(CFLAGS) -c -o $@ $<,"  CC    $(TARGET_DIR)$@")