help CI detect build failures

made 'make' and 'build-all.sh' exit with an error on fail,
so CI can hopefully detect it...
and added an intentional source bug to make it fail for testing purposes

bin/build-all.sh

@@ -66,4 +66,5 @@ echo "===== $PASS builds succeeded, $FAIL failed ====="
 #echo "PASS: $PASSED"
 if [ 0 != $FAIL ]; then
   echo "FAIL:$FAILED"
+  exit 1
 fi

hw/fireflies/arch

@@ -1 +1 @@
-attiny85
+attiny69

make

@@ -59,7 +59,7 @@ function main() {
       ;;
     dfp)
       shift
-      ./bin/dfp-install.sh "$@"
+      exec ./bin/dfp-install.sh "$@"
       ;;
     docs)
       make-docs
@@ -79,7 +79,7 @@ function main() {
       grep -E 'TODO:|FIXME:' **/*.[ch]
       ;;
     *)
-      ./bin/build-all.sh "$@"
+      exec ./bin/build-all.sh "$@"
       ;;
   esac
 }