abuild: mark failed builds as failed

abuild only created compile.status for successful builds,
but sometimes it's helpful to easily identify all failed
builds of a full run:

$ grep -l failed coreboot-builds/*/compile.status

Change-Id: Ic90280fb2e8cff1f8f558a2e67ffad741beddbdf
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Reviewed-on: http://review.coreboot.org/9964
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

util/abuild/abuild

@@ -254,6 +254,7 @@ function compile_target
 		junit "<failure type='BuildFailed'>"
 		junitfile make.log
 		junit "</failure>"
+		printf "failed\n" > compile.status
 		printf "$VENDOR/$MAINBOARD build FAILED after ${duration}s!\nLog excerpt:\n"
 		tail -n $CONTEXT make.log 2> /dev/null || tail -$CONTEXT make.log
 		failed=1