This adds the following types to fixed_width_ints behind appropriate platform cfgs:
* __int128
* __int128_t
* __uint128
* __uint128_t
and user_fpsimd_struct to arm64 android and linux.
Fixes it for at least the following targets:
* aarch64-unknown-linux-gnu
* arm-linux-androideabi
* arm-unknown-linux-gnueabihf
* arm-unknown-linux-gnueabihf
* arm-unknown-linux-musleabihf