Add cross-compilation to Aarch64 logic and investigate CI testing about parsec

[adamparco]

You could also leverage buildx to do emulated builds, or to point to a remote armv8 builder instance (AWS A1).

[hug-dev]

To cross-compile before, it used to be as easy as changing the Mbed Crypto library compiler in the build-conf.toml file and do the command: cargo build --target aarch64-unknown-linux-gnu
But with that now the compilation fails with the following issue:

          /usr/bin/ld: /home/hugdev01/dev/parsec/parsec/target/aarch64-unknown-linux-gnu/debug/deps/parsec-b832778a0064e80a.103gqkamrymphzyu.rcgu.o: Relocations in generic ELF (EM: 183)
          /usr/bin/ld: /home/hugdev01/dev/parsec/parsec/target/aarch64-unknown-linux-gnu/debug/deps/parsec-b832778a0064e80a.103gqkamrymphzyu.rcgu.o: Relocations in generic ELF (EM: 183)
          /usr/bin/ld: /home/hugdev01/dev/parsec/parsec/target/aarch64-unknown-linux-gnu/debug/deps/parsec-b832778a0064e80a.103gqkamrymphzyu.rcgu.o: Relocations in generic ELF (EM: 183)
          /usr/bin/ld: /home/hugdev01/dev/parsec/parsec/target/aarch64-unknown-linux-gnu/debug/deps/parsec-b832778a0064e80a.103gqkamrymphzyu.rcgu.o: Relocations in generic ELF (EM: 183)
          /usr/bin/ld: /home/hugdev01/dev/parsec/parsec/target/aarch64-unknown-linux-gnu/debug/deps/parsec-b832778a0064e80a.103gqkamrymphzyu.rcgu.o: Relocations in generic ELF (EM: 183)
          /usr/bin/ld: /home/hugdev01/dev/parsec/parsec/target/aarch64-unknown-linux-gnu/debug/deps/parsec-b832778a0064e80a.103gqkamrymphzyu.rcgu.o: Relocations in generic ELF (EM: 183)
          /usr/bin/ld: /home/hugdev01/dev/parsec/parsec/target/aarch64-unknown-linux-gnu/debug/deps/parsec-b832778a0064e80a.103gqkamrymphzyu.rcgu.o: Relocations in generic ELF (EM: 183)
          /usr/bin/ld: /home/hugdev01/dev/parsec/parsec/target/aarch64-unknown-linux-gnu/debug/deps/parsec-b832778a0064e80a.103gqkamrymphzyu.rcgu.o: error adding symbols: file in wrong format
          collect2: error: ld returned 1 exit status

It might be because the linker used is the system linker and not an Aarch64-toolchain linker?

[hug-dev]

Part of this issue is being addressed in #61: cargo build --target aarch64-unknown-linux-gnu will now cross-compile everything to this target.
To fix the issue above, the linker is precised in .cargo/config. I thought that the linker shipped with Rust installation could be used as well for cross-compiling but I think it does not support this target (or is not included?).

The remaining parts of this issue are related with testing:

• adding a CI job that cross-compile PARSEC for the Arm64 target (maybe buildx or cross could be used here)
• adding CI system where some of the tests are compiled and executed natively on Arm64 (Travis CI, AWS A1, Codefresh can be looked at)

[hug-dev]

#64 completed the first point above

[hug-dev]

We are going to set up a GitHub Actions self-hosted runner on an Arm Machine! That way we will only need little modification to our GH Actions workflows to make them run on Arm as well.

cf WorksOnArm/equinix-metal-arm64-cluster#190

[hug-dev]

Due to security problems about using GitHub Actions self-hosted runners, we decided to switch to Travis CI which has been enabled in #90