rules.mak: add more rules to avoid chaining

Really rule chaining is not a particularly expensive task, since
GNU Make caches the directory listing.  However it is easy to
avoid it for most files and for phony targets (one was missing).

After this patch, only "Makefile", "scripts/hxtool" and
"scripts/create_config" attempt to use chained rules.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Makefile.target

@@ -76,6 +76,7 @@ $(QEMU_PROG)-simpletrace.stp: $(BUILD_DIR)/trace-events-all
 else
 stap:
 endif
+.PHONY: stap
 
 all: $(PROGS) stap
 

rules.mak

@@ -7,6 +7,10 @@ MAKEFLAGS += -rR
 
 # Files with this suffixes are final, don't try to generate them
 # using implicit rules
+%/trace-events:
+%.hx:
+%.py:
+%.objs:
 %.d:
 %.h:
 %.c: