[ion-c-sys] builds on musl may be broken

[almann]

As per https://twitter.com/webbonet/status/1306114634043273223

The C didn't compile with musl for lambda and we didn't really wanted to force the project to compile C.

We should investigate this and make sure there isn't something in Ion C that is broken here (could be an amzn/ion-c issue).

[almann]

I whipped up a simple Dockerfile based on Alpine Linux (which uses musl) to try to debug this a bit:

https://gist.github.com/almann/e33183a06e32ad9933d013f7c19cb1c4

Here is the error I encountered:

thread 'main' panicked at 'Unable to find libclang: "the `libclang` shared library at /usr/lib/libclang.so.10 could not be opened: Dynamic loading not supported"', /home/user/.cargo/registry/src/github.com-1ecc6299db9ec823/bindgen-0.54.0/src/lib.rs:1959:31

I think part of the problem is this:

rust-lang/rust#34987

In theory cross-compiling should not be affected by this (e.g. targeting x86_64-unknown-linux-musl and delegating to musl-gcc and musl-g++ in the CMake delegation), but it needs to be tried and tested.

[almann]

Put together a Dockerfile based on Ubuntu 20.04 + musl gcc:

https://gist.github.com/almann/276c9eda7489cc39edfb69014d5bc12a

This builds and runs, so this would confirm that the problem seems to be with running the build with Rust's musl built toolchain, but not as a target.