Remove the insta-stable cfg(wasm)

[nagisa]

The addition of cfg(wasm) was an oversight on my end that turns out to have a number
of downsides:

• It was introduced as an insta-stable addition, forgoing the usual
  staging mechanism we use for potentially far-reaching changes;
• It is a breaking change for people who are using --cfg wasm either
  directly or via cargo for other purposes;
• It is not entirely clear if a bare wasm cfg is a right option or
  whether wasm family of targets are special enough to warrant
  special-casing these targets specifically.

As for the last point, there appears to be a fair amount of support for
reducing the boilerplate in specifying architectures from the same
family, while ignoring their pointer width. The suggested way forward
would be to propose such a change as a separate RFC as it is potentially
a quite contentious addition.

cc #83879 @devsnek

[rust-highfive]

r? @Mark-Simulacrum

(rust-highfive has picked a reviewer for you, use r? to override)

[devsnek]

I thought we were going to add a feature instead of removing this

[Mark-Simulacrum]

I haven't checked in terms of this actually reverting the change, but in terms of the specific code patch here seems OK; r=me.

I think we should remove this support for now, and then potentially re-add with a feature gate -- it looks like the code is minimal, and I'd rather not accidentally leave it in to hit stable :)

[nagisa]

I thought we were going to add a feature instead of removing this

That was what I thought as well, before I realized that adding cfg(wasm) is a breaking change. cfg(wasm) being a breaking change significantly reduces the chances of it being stabilized in the future as it is, which is why I opted for a removal rather than for implementing a feature gate.

I do encourage you to continue the discussion and propose to add something like this as a separate changeset. Sorry about that.

[Mark-Simulacrum]

@bors r+

[bors]

📌 Commit 54dc7ce has been approved by Mark-Simulacrum

[bors]

⌛ Testing commit 54dc7ce with merge 69e1d22...

[bors]

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing 69e1d22 to master...