x86_64_elf_*: https://github.com/altkatz/homebrew-gcc_cross_compilers
grub.rb: https://github.com/nativeos/homebrew-i386-elf-toolchain/blob/master/Formula/i386-elf-grub.rb
objconv.rb: https://github.com/hawkw/homebrew-grub/blob/master/Formula/objconv.rb Change SHA256
