libuv: Avoid posix_spawn on macOS < 10.8

Restore the effect of commit e3e2ef1964 (libuv: Avoid posix_spawn on
macOS < 10.8, 2024-03-25, v3.28.5~6^2) after it was removed by merge
conflicts with libuv's switch to preferring `posix_spawn`.

Utilities/cmlibuv/src/unix/process.c

@@ -534,6 +534,9 @@ static void uv__spawn_init_posix_spawn(void) {
    * Unices in that it returns 0 instead of EACCES or ENOENT for paths
    * that don't exist. See https://github.com/libuv/libuv/issues/5240.
    */
+#elif defined(__APPLE__) && MAC_OS_X_VERSION_MIN_REQUIRED < 1080
+  /* posix_spawn on macOS < 10.8 has been observed to cause
+     kernel panics and/or resource exhaustion.  Always use fork.  */
 #else
 #if !defined(__linux__) && !defined(_AIX) && !defined(__PASE__)
   posix_spawn_works = 1;