build-script-impl: add support for freebsd-arm64

Lack of this line causes a build error: `Unknown host tools target: freebsd-arm64`.

Author: MaxDesiatov

utils/build-script-impl

@@ -452,7 +452,8 @@ function should_execute_host_actions_for_phase() {
 function verify_host_is_supported() {
     local host="$1"
     case ${host} in
-      freebsd-x86_64            \
+      freebsd-arm64             \
+      | freebsd-x86_64          \
       | openbsd-amd64           \
       | cygwin-x86_64           \
       | haiku-x86_64            \