Use build-std=core on a custom targets automatically

[nazar-pc]

When working with a custom target, it basically requires everyone to add annoying -Z build-std=core to CLI all the time. I don't know how many use cases there are where not having even core makes a lot of sense, but to me it would be way more ergonomic if it was compiled for custom targets (and Tier 3 targets?) automatically by default.

Not sure if this is the right repo for such request, feel free to move or direct me to a better place to discuss this.

[weihanglo]

You might want to put it in .cargo/config.toml, so no need to specify it every time.

[nazar-pc]

Sure, I'm just thinking about what the default should be. If it is not usable without build-std anyway then what is the point, right?

[ehuss]

Thanks for the report! I'm going to close as a duplicate of #43. We're still exploring what the eventual mechanism will be for enabling build-std, and whether or not that will automatic in any way.