Improves scripts and add docker image

[henrybear327]

This commit adds a docker image that provides the pre-configured environment, which is capable of executing the rv32emu tests, to the users. It can also reduce hassles when working on the M1 machines for development.

Figuring out the dockerfile actually took longer than expected, and here are the 2 main issues (there are also copious of comments in the dockerfile):

• The gcc-riscv64-unknown-elf compiler installed from apt will cause make arch-test to fail with error unsupported ISA subset 'z', thus, we build from scratch using the version [here].(ttps://github.com/sysprog21/rv32emu/blob/master/.ci/riscv-toolchain-install.sh).
• The reference emulator in the repo is of x86 architecture, so for the aarch64 (M1 machine), we need to build from sail-riscv source. Interestingly, it's a known issue that the recent commits will fail to compile. But in any case, for this dockerfile, I am using the commit from sail-riscv which is around the time that the commit of the reference emulator happened on rv32emu, which has no problem building and completing tests.

Reference:

• Add Dockerfile as advanced preparation for CI #40

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[jserv]

Thank @henrybear327 for contributing!