add clang as a common build tool

[anatawa12]

Closes #174

This PR adds clang as a common build tool.
The libclang will be used by bindgen so It's better to have clang on all platforms so I add to common.sh

This works for bindgen for the following targets with ffmpeg-next of libavformat, libavcodec, and libavutil with my built ffmpeg binaries:

• x86_64-pc-windows-gnu
• x86_64-unknown-linux-musl

I couldn't test x86_64-unknown-linux-gnu because of #455

#455 error message. This will be happened without this PR (with the image from DockerHub)

   Compiling libc v0.2.107
   Compiling ffmpeg-sys-next v4.4.0
error: failed to run custom build command for `libc v0.2.107`

Caused by:
  process didn't exit successfully: `/target/release/build/libc-e4387d0c49bcd20f/build-script-build` (exit status: 1)
  --- stderr
  /target/release/build/libc-e4387d0c49bcd20f/build-script-build: /lib64/libc.so.6: version `GLIBC_2.18' not found (required by /target/release/build/libc-e4387d0c49bcd20f/build-script-build)
warning: build failed, waiting for other jobs to finish...
error: build failed

[michaelsproul]

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/)

[JEnoch]

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.

[michaelsproul]

Thank you @JEnoch!

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

My Docker files are here for reference.

[timstokman]

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.

[anatawa12]

I've changed the library to libclang-dev.

[Emilgardis]

LGTM

However, CI is broken

r=me when fixed

[Emilgardis]

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

[reitermarkus]

bors r+

[bors]

Build succeeded:

• conclusion