Fix WASI build

[alex-semenyuk]

No description provided.

[emmatyping]

  --- stderr
  /usr/include/features-time64.h:20:10: fatal error: 'bits/wordsize.h' file not found

  thread 'main' (22339) panicked at Modules/cpython-sys/build.rs:61:10:
  Unable to generate bindings: ClangDiagnostic("/usr/include/features-time64.h:20:10: fatal error: 'bits/wordsize.h' file not found\n")
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
make: *** [Makefile:3501: cpython-sys] Error 101

Looks like the system headers are not found correctly by bindgen, I wonder if we need to find wasi-libc/wasi-sdk ourselves. Ideally we'd make sure it's the same as the one found in https://github.com/python/cpython/blob/main/Tools/wasm/wasi/__main__.py, perhaps that script can pass an environment variable the build.rs can read?

[emmatyping]

It looks like the WASI build script already sets WASI_SDK_PATH and WASI_SYSROOT https://github.com/Rust-for-CPython/cpython/blob/3.15-rust-in-cpython/Tools/wasm/wasi/__main__.py#L285-L286, perhaps it'd be better to just update the build.rs script to check if WASI_SYSROOT is set and add the argument there? Alternatively, you could set this environment variable in the WASI build script.

[alex-semenyuk]

yes, it doesn't help, the error is not in this

[emmatyping]

Yeah, I misunderstood the error. With WASI, modules are statically linked into libpython, so the error is that the linker isn't finding the PyInit__base64 symbol despite the linker hacks we have in place. In CPython modules can be build either statically or dynamically linked to libpython (which can depend on the platform. Finding a good solution to that seems important.