abuild: only rebuild boards if requested or after a broken build

That used to be the behaviour, and it's quite useful to incrementally
fix bugs across the tree.

Change-Id: I3e30cbdcf01631bc29f892054caa3babb0969beb
Signed-off-by: Patrick Georgi <patrick.georgi@secunet.com>
Reviewed-on: http://review.coreboot.org/1888
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

util/abuild/abuild

@@ -298,6 +298,12 @@ function build_target
 	CONFIG=$3
 	TARCH=$( architecture $VENDOR $MAINBOARD )
 
+	if [ "`cat $TOP/$TARGET/${VENDOR}_${MAINBOARD}/compile.status 2>/dev/null`" = "ok" -a \
+		"$buildall" = "false" ]; then
+		printf "Skipping $VENDOR/$MAINBOARD; (already successful)\n"
+		return
+	fi
+
 	# default setting
 
 	CC="${CROSS_COMPILE}gcc"