Build script fails on Alpine / muslibc

[chrysn]

When building on Alpine (which is muslibc based), building Rust based RIOT applications fails:

  --- stderr
  thread 'main' panicked at 'Unable to find libclang: "the `libclang` shared library at /usr/lib/libclang.so.13.0.1 could not be opened: Dynamic loading not supported"', /root/.cargo/registry/src/github.zerozr99.workers.dev-1ecc6299db9ec823/bindgen-0.60.1/src/lib.rs:2172:31
  stack backtrace:
     0: rust_begin_unwind
               at /rustc/d394408fb38c4de61f765a3ed5189d2731a1da91/library/std/src/panicking.rs:584:5
     1: core::panicking::panic_fmt
               at /rustc/d394408fb38c4de61f765a3ed5189d2731a1da91/library/core/src/panicking.rs:142:14
     2: core::result::unwrap_failed
               at /rustc/d394408fb38c4de61f765a3ed5189d2731a1da91/library/core/src/result.rs:1814:5
     3: core::result::Result<T,E>::expect
     4: core::ops::function::FnOnce::call_once
     5: lazy_static::lazy::Lazy<T>::get::{{closure}}
     6: std::sync::once::Once::call_once::{{closure}}
     7: std::sync::once::Once::call_inner
               at /rustc/d394408fb38c4de61f765a3ed5189d2731a1da91/library/std/src/sync/once.rs:434:21
     8: std::sync::once::Once::call_once
     9: <bindgen::ensure_libclang_is_loaded::LIBCLANG as core::ops::deref::Deref>::deref
    10: bindgen::ensure_libclang_is_loaded
    11: bindgen::Bindings::generate
    12: bindgen::Builder::generate
    13: build_script_build::main
    14: core::ops::function::FnOnce::call_once
  note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
make: *** [/tmp/RIOT/makefiles/cargo-targets.inc.mk:44: /tmp/RIOT/examples/rust-hello-world/bin/microbit-v2/target/thumbv7em-none-eabihf/release/librust_hello_world.a] Error 101

Reproducing

I've tested this inside the container set up per immunant/c2rust#724 with maribu's resolution (RUSTFLAGS=-Ctarget-feature=-crt-static cargo install --locked c2rust) with an extra of (the former is generally needed for RIOT, the latter target specific and make would have told us later anyway):

$ apk add git gcc-arm-none-eabi newlib-arm-none-eabi
$ rustup target add thumbv7em-none-eabihf

Then run (ideally after RIOT-OS/RIOT#18904 is in, or apply it manually):

$ make -C examples/rust-hello-world BOARD=microbit-v2

Towards fixing

When switching riot-sys's bindgen dependency to /static (btw, we don't really use the default features it seems...), the build script instead segfaults in a way similar to rust-lang/rust-bindgen#2333:

error: failed to run custom build command for `riot-sys v0.7.9 (/tmp/riot-sys)`

Caused by:
  process didn't exit successfully: `/tmp/RIOT/examples/rust-hello-world/bin/microbit-v2/target/release/build/riot-sys-1835746e88917b5e/build-script-build` (signal: 11, SIGSEGV: invalid memory reference)

CC @maribu who originally found this.

[edit: more precise setup instructions]