Add support for AArch64/ARMv8/ARM64
These patches add support for AArch64/ARMv8/ARM64 64-bit ARM processor.
base-system, base-chroot{,-musl} and base-devel cross-compiled successfully
at once (given coreutils-doc has been added to the repo already).
Both glibc and musl are supported.
Uncommented lines of common/environment/configure/autoconf_cache/aarch64-linux
have not yet been verified/needed.
Light testing has been performed on Linaro QEMU "genericarmv8" with
Kernel 3.19, due to lack of real hardware.
b03de9bc1c