Added crosscompile toolchain file for aarch64.

[nayakned]

No description provided.

[nayakned]

Try running.

$ sudo apt install gcc-aarch64-linux-gnu
$ cmake .. -DCMAKE_TOOLCHAIN_FILE=../aarch64.toolchain
$ make

Artifacts can tested on a Pi or qemu+Docker.

[SebastianSchildt]

Seems to work.

Interesting observation: This needs to be done on the FIRST run of cmake in an empty build dir. If cmake (with or without the option) had already been run, I get

cmake .. -DCMAKE_TOOLCHAIN_FILE=../aarch64.toolchain
-- Configuring done (0.0s)
-- Generating done (0.0s)
CMake Warning:
  Manually-specified variables were not used by the project:

    CMAKE_TOOLCHAIN_FILE


-- Build files have been written to: /home/sebastian/Open1722/build

Maybe mention in the docs, it works only on a "fresh" cmake run

Anyway, looks good to me, but will not merge as @nayakned still seems to be tinkering with cmake, so not sure this is obsolete