check return code of make in tools/make_all_examples

tools/make_all_examples

 saved_pwd_before_making=$PWD
 for file in `find example tools -name Makefile`; do
     cd $(dirname $file)
-    echo -e "\n[$file]"
-    make -sj4
+    echo
+    echo "[$file]"
+    if ! make -sj4; then
+        exit 1
+    fi
     cd $saved_pwd_before_making
 done