chore: Use stable Rust 1.38.0 and update Linux headers for x86_6…

[ghost]

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[LucioFranco]

@a-rodin can we break out the toolchain build part of this and the part that adds the dependencies for vector? We could probably at some point extract our musl toolchain so that others can use it. What do you think?

[ghost]

@LucioFranco Actually this builder is already not very Vector-specific. The only part that can be considered external is OpenSSL, which can be extracted easily (but those who want to use OpenSSL available for C libraries would need to do the same patching as we do here in order to compile it).

The idea of making it available for use by others is great. I think it might be worth to decide how is it going to be shared to clarify requirements for that toolchain image. I see three approaches:

• keep it in Vector's repository, but separated and published to Docker Hub;
• keep it in a separate repository;
• try to push it to be an official Rust musl/libc++/clang toolchain image.

[LucioFranco]

@a-rodin I created #946 to track this, we can move discussion there.

[LucioFranco]

We need to build the image and push it before we merge this PR.

[LucioFranco]

@a-rodin Image is being built right now. I moved the patch into the root dir of the builder images since that is where docker loads the context when running build-ci-images.sh.

[LucioFranco]

New image has been pushed.