Update Wiki to Use New toolchain

[CRKatri]

I have recently released a new arm64e toolchain for use with theos, it is available for Debian Buster, Ubuntu 18.04, and Ubuntu 20.04, although the ubuntu toolchains should work on a wide variety of distros. They contain updated cctools and libtapi. It is compatible for both objc and swift development. This will allow swift development to be done from Linux.

It's tools are updated from @sbingner's arm64e llvm/clang toolchain and @kabiroberai's swift 4 toolchain.

[kabiroberai]

There's two approaches to be considered here:

1. Continue keeping the Clang and Swift toolchains separate, since that way users can save space if they don't plan on using Swift. At the moment, clang is still being duplicated because swiftc comes with its own copy, but this could be remedied by specifying -tools-directory to swiftc and pointing it at the other toolchain.
2. Use a single toolchain with everything in it. This has the benefit of not needing to worry about Swift possibly using a different Clang, and can also make sure that both Clang and Swift are compiled with the same llvm version etc so that there isn't any discrepancy in, say, the supported tapi version.

I'm not sure which is better tbh, but I'm interested in hearing what others have to say about this.