I ran into a similar issue while trying to run bindgen under cross but it wasn't fixed by installing clang because cross uses Ubuntu 16.04 which only includes Clang 3.8 (I think I need 3.9+). There's also no PPA available for Clang 3.9 on 16.04:

Mar 28th 2021 - Ubuntu Xenial (16.04) disabled (EOL)

(from https://apt.llvm.org/)

I also had issues with Clang 3.8 which is the packaged version for Ubuntu 16.04.
Thus I followed @Nnubes256's suggestion in #257 and made custom images installing Clang 12 and defining appropriate --sysroot option for Clang via BINDGEN_EXTRA_CLANG_ARGS.

If any help the images are available as jenoch/rust-cross and the Dockerfiles are in https://github.com/JEnoch/rust-cross-clang/.

I only made images for ARMs and x86_64+musl so far. I'm not sure if/how what I did can be adapted as a PR in here for all Docker images.

Thank you @JEnoch!

I can confirm that the same technique works on x86_64 with glibc!

My Docker files are here for reference.

To get bindgen working, all I did was use this docker image:

FROM rustembedded/cross:armv7-unknown-linux-gnueabihf-0.2.1

RUN apt-get update && apt-get install --assume-yes libclang-3.9-dev

Just libclang-3.9-dev is enough, no PPA necessary.

I've changed the library to libclang-dev.

Remaining errors are due to a timeout also observed in #609

bors r+

Build succeeded:

• conclusion