Support Apple Silicon

[quentinlesceller]

Equivalent of mimblewimble/grin#3545 for grin-wallet.
Currently Grin-Wallet does not build on Apple Silicon (ARM M1). For two reasons:

• Ring must be updated to >="0.16.16". Easy fix with cargo update -p ring.
• croaring-rs (in fact croaring-sys does not compile for an unknown reason. See Failed to build on Apple Silicon RoaringBitmap/croaring-rs#66. EDIT: Fixed by Update bindgen to v0.56.0 RoaringBitmap/croaring-rs#67. Wondering if we still need that fork of croaring btw.

[trevyn]

Ran the grin-wallet dual of mimblewimble/grin#3545 (comment) on aarch64-apple-darwin as such:

git clone -b trevyn-croaring-defork https://github.com/trevyn/grin-wallet.git
cd grin-wallet
cargo update -p ring
cargo build
cargo build --release
cargo test --all

All worked on:

rustc 1.50.0 (cb75ad5db 2021-02-10)
rustc 1.51.0-beta.7 (80eddb935 2021-03-17)
rustc 1.52.0-nightly (36f1f04f1 2021-03-17)

Will submit PR when mimblewimble/grin#3596 is merged.

[quentinlesceller]

We now support Apple Silicon! Thanks @trevyn