move modules necessary to implement a GC to core.gc

[rainers]

This allows compiling new GC implementations without requiring adding an import path to druntime/src.

Not sure if this is better than just adding the 3 gc-files to the import folder as is. Comments?

[dlang-bot]

Thanks for your pull request, @rainers!

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[wilzbach]

Couldn't this file import the declarations from gc.proxy instead of defining the headers again?

[rainers]

Not sure what you mean. Do you prefer a cyclic dependency and a public import in gc.proxy over a simple import of the public module?

[wilzbach]

Do you prefer a cyclic dependency

Ah sorry. Nevermind then.

[rainers]

Ah, I didn't see the gc_* declarations in the diff. I think we have these declarations elsewhere too, e.g. core.memory. IIRC this is done to fake some attributes.

[wilzbach]

Do we want to expose this to the user and docs? Maybe make everything package for now?

[rainers]

I think a GC implementation should be able to use the configuration even if it does not support all the values in there.

[rainers]

Maybe make everything package for now?

That would disallow accessing these modules from package gc AFAICT.

[wilzbach]

That would disallow accessing these modules from package gc AFAICT.

Fair enough.