build.sh: bail out if 'make clean' fails

build.sh

@@ -202,6 +202,8 @@ for target in ${TARGETS} ; do
 	# prepare build environment for our current target
 	progress "Preparing build environment for target ${target}."
 	[ "${DIRCLEAN}" -eq "0" ] && make clean
+	[ "$?" -eq "0" ] || abort "Unable to clean environment for target-platform ${target}."
+
 	make -j ${MAKEJOBS} prepare-target ${MAKE_PARAM}
 	[ "$?" -eq "0" ] || abort "Unable to build environment for target-platform ${target}."