Reproducer for "skip" conditions differences between pixi build and rattler-build

The goal of the recipe is to

• build 2 packages when not cross-compiling: one platform dependent and one noarch (stubs)
• build only the compiled library package if cross-compiling

pixi build doesn't behave similarly to rattler-build build with skip selector syntax using build and target platforms:

skip:
  - build_platform != target_platform

With pixi build, only 1 package is build, whether --target-platform=linux-aarch64 is passed. With rattler-build build the condition is respected:

# builds a single package
pixi build
# builds a single package too
pixi build --target-platform=linux-aarch64
# builds 2 packages
rattler-build build -r recipe/recipe.yml
# builds 1 package
rattler-build build -r recipe/recipe.yml --target-platform=linux-aarch64

With the selector updated to

skip:
  - build_platform == "linux-aarch64"

pixi build --target-platform=linux-aarch64 builds a single package. It looks like the build_platform is used as the target_platform.