WIP: visionOS build container

[akien-mga]

• Depends on and includes Update various toolchains for 4.5 #151.

Initial WIP on adding support for compiling for visionOS using cctools-port, like we do for iOS.

For now this only adds support for extracting the XROS and XRSimulator SDKs from the Xcode xip, so that's not doing much.

To (attempt to) make a build image that can target visionOS, we should copy Dockerfile.ios to a new Dockerfle.visionos and see how to change it to target this related platform.

The work done by @naithar for tvOS a few years ago should be helpful:

• tvOS build support #71

Notably we might indeed need to write a custom wrapper, or patch cctools-port's current one in https://github.com/tpoechtrager/cctools-port/tree/1024.3-ld64-955.13/usage_examples/ios_toolchain to make it target visionOS instead of iOS.

I note that there's at least one user of cctools-port who tried to do that and had some issue:

• XROS Support ? tpoechtrager/cctools-port#149

I don't know if we'd run into the same, and if it's something we can help fix upstream.

CC @bruvzg @stuartcarnie @BastiaanOlij

[bruvzg]

Notably we might indeed need to write a custom wrapper, or patch cctools-port's current one in

Probably, since it's adding -miphoneos-version-min and it should be replaced with -mtargetos=xros2.0. Platforms should be similar, so at worst case, I would expect patching LC_BUILD_VERSION (like we did with iOS simulator).