For now, we need to use a custom rust toolchain for this. Apparently all
alternatives to this don't work. -Zbuild-std doesn't work with panic=abort
(rust-lang/cargo#7359)
and my attempts to use a custom sysroot with either
https://github.com/RalfJung/rustc-build-sysroot/ or
https://github.com/DianaNites/cargo-sysroot/  seem to hit the same problem
as with `-Zbuild-std`. Thus, I think the only reasonable way to go is to
build the sysroot from the rust source directory. Perhaps we can eventually
approach this by copying the `lib/rustlib/wasm32-unknown-emscripten/lib/`
folder out of the build of the rust compiler on top of a nightly install of
the compiler. For now, there is the additional problem that we need this
patch to fix unwind=abort:
rust-lang/rust#135450

I got my copy of the rust compiler by checking out this commit:
hoodmane/rust@052ba16
two commits ahead of the rust main branch and running:
```
./x build --stage 2 --target x86_64-unknown-linux-gnu,wasm32-unknown-emscripten
```

Rollup of 10 pull requests

Successful merges:

 - rust-lang#134498 (Fix cycle error only occurring with -Zdump-mir)
 - rust-lang#134977 (Detect `mut arg: &Ty` meant to be `arg: &mut Ty` and provide structured suggestion)
 - rust-lang#135390 (Re-added regression test for rust-lang#122638)
 - rust-lang#135393 (uefi: helpers: Introduce OwnedDevicePath)
 - rust-lang#135440 (rm unnecessary `OpaqueTypeDecl` wrapper)
 - rust-lang#135441 (Make sure to mark `IMPL_TRAIT_REDUNDANT_CAPTURES` as `Allow` in edition 2024)
 - rust-lang#135444 (Update books)
 - rust-lang#135450 (Fix emscripten-wasm-eh with unwind=abort)
 - rust-lang#135452 (bootstrap: fix outdated feature name in comment)
 - rust-lang#135454 (llvm: Allow sized-word rather than ymmword in tests)

r? `@ghost`
`@rustbot` modify labels: rollup

Rollup merge of rust-lang#135450 - hoodmane:wasm-eh-abort-fix, r=workingjubilee

Fix emscripten-wasm-eh with unwind=abort

If we build the standard library with wasm-eh then we need to link with `-fwasm-exceptions` even if we compile with `panic=abort`.

Without this change, linking a `panic=abort` crate fails with: `undefined symbol: __cpp_exception`.

Followup to rust-lang#131830.

r? workingjubilee

Rollup of 10 pull requests

Successful merges:

 - rust-lang#134498 (Fix cycle error only occurring with -Zdump-mir)
 - rust-lang#134977 (Detect `mut arg: &Ty` meant to be `arg: &mut Ty` and provide structured suggestion)
 - rust-lang#135390 (Re-added regression test for rust-lang#122638)
 - rust-lang#135393 (uefi: helpers: Introduce OwnedDevicePath)
 - rust-lang#135440 (rm unnecessary `OpaqueTypeDecl` wrapper)
 - rust-lang#135441 (Make sure to mark `IMPL_TRAIT_REDUNDANT_CAPTURES` as `Allow` in edition 2024)
 - rust-lang#135444 (Update books)
 - rust-lang#135450 (Fix emscripten-wasm-eh with unwind=abort)
 - rust-lang#135452 (bootstrap: fix outdated feature name in comment)
 - rust-lang#135454 (llvm: Allow sized-word rather than ymmword in tests)

r? `@ghost`
`@rustbot` modify labels: rollup