We need to apply some bug fixes that were merged to wasi-libc because wasi-sdk-20
is about half a year old.
It is a temporary solution and the code will be removed when wasi-sdk 21 is released.
We need to make a test that runs longer than the tests we had before to check
some problems that might happen after running for some time (e.g. memory
corruption or something else).
`wasi-sdk-20` pre-release can be used to avoid building `wasi-libc` to enable threads.
It's not possible to use `wasi-sdk-20` pre-release on Ubuntu 20.04 because of
incompatibility with the glibc version:
```bash
/opt/wasi-sdk/bin/clang: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.34' not found
(required by /opt/wasi-sdk/bin/clang)
```
