Unimplement unsized_locals
Implements https://github.com/rust-lang/compiler-team/issues/630
Tracking issue here: https://github.com/rust-lang/rust/issues/111942
Note that this just removes the feature, not the implementation, and does not touch `unsized_fn_params`. This is because it is required to support `Box<dyn FnOnce()>: FnOnce()`.
There may be more that should be removed (possibly in follow up prs)
- the `forget_unsized` function and `forget` intrinsic.
- the `unsized_locals` test directory; I've just fixed up the tests for now
- various codegen support for unsized values and allocas
cc ``@JakobDegen`` ``@oli-obk`` ``@Noratrieb`` ``@programmerjake`` ``@bjorn3``
``@rustbot`` label F-unsized_locals
Fixesrust-lang/rust#79409
Implement `//@ needs-target-std` compiletest directive
Closesrust-lang/rust#141863.
Needed to unblock rust-lang/rust#139244 and rust-lang/rust#141856.
### Summary
This PR implements a `//@ needs-target-std` compiletest directive that gates test execution based on whether the target supports std or not. For some cases, this should be preferred over e.g. some combination of `//@ ignore-none`, `//@ ignore-nvptx` and more[^none-limit].
### Implementation limitation
Unfortunately, since there is currently [no reliable way to determine from metadata whether a given target supports std or not](https://github.com/rust-lang/rust/issues/142296), we have to resort to a hack. Bootstrap currently determines whether or not a target supports std by a naive target tuple substring comparison: a target supports std if its target tuple does *not* contain one of `["-none", "nvptx", "switch"]` substrings. This PR simply pulls that hack out into `build_helpers` to avoid reimplementing the same hack in compiletest, and uses that logic to inform `//@ needs-target-std`.
### Auxiliary changes
This PR additionally changes a few run-make tests to use `//@ needs-target-std` over an inconsistent combination of target-based `ignore`s. This should help with rust-lang/rust#139244.
---
r? bootstrap
[^none-limit]: Notably, `target_os = "none"` is **not** a sufficient condition for "target does not support std"
Rewriting git history is something that is often difficult for new contributors,
and we're already explaining the `<foo>` placeholder syntax,
so I think it makes sense to be explicit about what exactly the paths mean.
The rustc-dev-guide Cronjob Bot
Tshepang Mbambo
Matthias Krüger
xizheyin
mejrs
lolbinarycat
Jieyou Xu
cyrgani
León Orell Valerian Liehr
onur-ozkan
许杰友 Jieyou Xu (Joe)
Rageking8
Stan Manilov
Yukang
nora