* Add SERENITY_ARCH option to CMake for selecting the target toolchain
* Port all build scripts but continue to use i686
* Update GitHub Actions cache to include BuildIt.sh
Added a script to build QEMU from source as part of the Toolchain.
The script content could be in BuildIt.sh but has been put in
a seperate file to make the build optional.
Added PATH=$PATH to sudo calls to hand over the Toolchain's PATH
setup by UseIt.sh. This enabled the script's to use the QEMU
contained in the SerenityOS toolchain.
Deleted old documentation in Meta and replaced it by a new
documentation in the Toolchain folder.
