build-sys hack: ensure target directory is there

By removing some unnest-vars calls, we miss some directory creation
that may be required by some/dir/object.d.

This will go away once everything is converted to Meson.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

rules.mak

@@ -66,6 +66,7 @@ expand-objs = $(strip $(sort $(filter %.o,$1)) \
                   $(filter-out %.o %.mo,$1))
 
 %.o: %.c
+	@mkdir -p $(dir $@)
 	$(call quiet-command,$(CC) $(QEMU_LOCAL_INCLUDES) $(QEMU_INCLUDES) \
 	       $(QEMU_CFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) $($@-cflags) \
 	       -c -o $@ $<,"CC","$(TARGET_DIR)$@")