* Bumps brotli version to incorporate a fix for some GCC warnings which
get promoted to errors.
* Switches from wee8 to WAMR because it's easier to make it build
sensibly on a range of GCC versions that aren't just "whatever ships
with Ubuntu LTS".
* Adds a patch for WAMR's build in Envoy because it won't build properly
under Linux aarch64, since WAMR doesn't detect aarch64 unless it's on
macOS.
