util/futility: trivial - Add distclean target

The what-jenkins-does build runs distclean when building the utilities.
It doesn't fail the build if distclean fails, but it generates a
scary warning.

Change-Id: Iac90958951976ed326a89ef2b5f2d9f17f9f2d6b
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/13888
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
diff --git a/util/futility/Makefile b/util/futility/Makefile
index 3ce45ed..f00e2eb 100644
--- a/util/futility/Makefile
+++ b/util/futility/Makefile
@@ -12,6 +12,8 @@
 	$(RM) $(objutil)/futility/futility
 	$(RM) -r $(objutil)/futility/build
 
+distclean: clean
+
 ifneq ($(V),1)
 ifneq ($(Q),)
 .SILENT: