Add `binary_format` to rustc target specs

[Noratrieb]

There are some places in rustc that need to know the binary format of the target (to generate object files). It would be good to have this as a property on the target spec to avoid needing to have ad-hoc logic for it.

See #135695 (comment)

[yegeunyang]

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[yegeunyang]

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[Pyr0de]

Hey,
I would like to give this issue a go. Could you please provide me with some more info about it?

Do I need to add a new field in Target that has the BinaryFormat?

[Noratrieb]

Yes. You need to create a new field in the target with the binary format (create a new enum for this, don't use the one from the object crate). You will need to do a few other things as well but you may be able to figure that out from test failures and other code in the area.

To populate them for existing targets, you can find the existing logic where I linked it.

[Pyr0de]

For the new enum, should it contain all the enum variants from BinaryFormat(object crate) or just the ones given in the logic mentioned in the OP?

To populate the existing targets, do I manually set the binary_format for each target in compiler/rustc_target/src/spec/targets or can I just use a function and call it in each file?

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