Building aarch64 image fails due to gfortran not being available

[astapleton]

Checklist

• I've looked through the issues and pull requests for similar reports

Describe your issue

Building the aarch64 Docker image on Mac M1/M2 fails due to a missing package error for gfortran. ie. running this:

docker build -f Dockerfile.aarch64-unknown-linux-gnu -t ghcr.io/cross-rs/aarch64-unknown-linux-gnu:main https://github.com/cross-rs/cross.git#main:docker

results in this error:

Unable to locate package gfortran-aarch64-linux-gnu

which then fails the image creation.

It seems like this was introduced in this commit: 6ab0e7c

I also reproduced this on an x86_64 Windows host when specifying --platform linux/arm64 during the build step.

What target(s) are you cross-compiling for?

No response

Which operating system is the host (e.g computer cross is on) running?

• macOS
• Windows
• Linux / BSD
• other OS (specify in description)

What architecture is the host?

• x86_64 / AMD64
• arm32
• arm64 (including Mac M1)

What container engine is cross using?

• docker
• podman
• other container engine (specify in description)

cross version

cross 0.2.5

Example

docker build -f Dockerfile.aarch64-unknown-linux-gnu -t ghcr.io/cross-rs/aarch64-unknown-linux-gnu:main https://github.com/cross-rs/cross.git#main:docker

Additional information / notes

Building with an older commit works:

docker build -f Dockerfile.aarch64-unknown-linux-gnu -t ghcr.io/cross-rs/aarch64-unknown-linux-gnu:main https://github.com/cross-rs/cross.git#c87a52a60dbcde069714a8d2ed51570e7fc23cf9:docker