Update backends/arm/scripts/build_executorch.sh

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: perheld

backends/arm/scripts/build_executorch.sh

@@ -98,7 +98,9 @@ if [[ ${is_linux_musl} -eq 1 ]]; then
         --preset arm-ethosu-linux \
         -DPYTHON_EXECUTABLE=$(which python3)
 else
-    cmake "${cmake_args[@]}" --preset arm-baremetal -B${et_build_dir}
+    cmake -S "${et_root_dir}" -B "${et_build_dir}" \
+        "${cmake_args[@]}" \
+        --preset arm-baremetal
 fi
 
 parallel_jobs="$(get_parallel_jobs)"