Avoid installing deprecated Python 2 from Homebrew

[MaxDesiatov]

brew install python@2 now fails for me locally due to Homebrew/homebrew-core#49796, not sure how it still runs fine on CI, probably due to caches not being cleaned up as frequently.

I hope relying on system-installed Python should work fine.

[kateinoigakukun]

Running lit tests on Linux VM on GitHub Actions takes too long time.
It reached the execution time limit of GitHub Actions 😢

Each job in a workflow can run for up to 6 hours of execution time. If a job reaches this limit, the job is terminated and fails to complete. There are no time limits for self-hosted runners.

https://help.github.com/en/actions/getting-started-with-github-actions/about-github-actions#usage-limits

We have to consider another way to run the lit tests continuously, but for the moment, I think it's OK to stop running test and remove -t flag from build-script.

[MaxDesiatov]

I was wondering whether we can precompile llvm and clang as a job in our llvm-project fork. Maybe as a Docker image that can be then used to run jobs in this repo, based on swiftwasm-linux-builder?

[kateinoigakukun]

I think it's great worth to prepare pre-built llvm binary on Docker 👍
Only my concern is whether ninja cache system works expectedly.