Add support for ARM64 builds

[m-simonelli]

Given the rising popularity of ARM devices (i.e. M1, linux aarch64), we should support ARM64 builds

[eleanor-em]

Are there any known roadblocks to this? I'm happy to give some things a try since I have a bunch of arm64 boxes ready to go.

[morganava]

For arm64 linux, it should be a relatively simple (though time consuming) task of porting over the arm64 build configurations from tor-browser-build. My plan was to just wait until Tor Browser added support for arm macOS builds and then port over there changes (which should be happening sometime this year)

[morganava]

aarch64 is now a supported build target for macOS with the rewerite