Union fields may now never have a type with attached destructor.
This for example allows unions to use arbitrary field types only by
wrapping
them in ManuallyDrop.

The stable rule remains, that union fields must be Copy. We use the new
rule for the `untagged_union` feature.

See RFC 2514.

Note for ui tests:
We can't test move out through Box's deref-move since we can't
have a Box in a union anymore.

Cases where it would trigger are now hard errors.

Co-Authored-By: Mazdak Farrokhzad <twingoow@gmail.com>

Co-Authored-By: Mazdak Farrokhzad <twingoow@gmail.com>

Co-Authored-By: Mazdak Farrokhzad <twingoow@gmail.com>

Co-Authored-By: Mazdak Farrokhzad <twingoow@gmail.com>

…ing iterators

…type

With rust-lang#65251 landed there's no need to build two LLVM backends and ship
them with rustc, every target we have now uses the same LLVM backend!

This removes the `src/llvm-emscripten` submodule and additionally
removes all support from rustbuild for building the emscripten LLVM
backend. Multiple codegen backend support is left in place for now, and
this is intended to be an easy 10-15 minute win on CI times by avoiding
having to build LLVM twice.

… r=RalfJung

Change untagged_unions to not allow union fields with drop

This is a rebase of rust-lang#56440, massaged to solve merge conflicts and make the test suite pass.

Change untagged_unions to not allow union fields with drop

Union fields may now never have a type with attached destructor. This for example allows unions to use arbitrary field types only by wrapping them in `ManuallyDrop` (or similar).

The stable rule remains, that union fields must be `Copy`. We use the new rule for the `untagged_union` feature.

Tracking issue: rust-lang#55149

make is_power_of_two a const function

This makes `is_power_of_two` a const function by using `&` instead of short-circuiting `&&`; Rust supports bitwise `&` for `bool` and short-circuiting is not required in the existing expression.

I don't think this needs a const-hack label as I don't find the changed code less readable, if anything I prefer that it is clearer that short circuiting is not used.

@oli-obk

…end, r=Mark-Simulacrum

Remove `src/llvm-emscripten` submodule

With rust-lang#65251 landed there's no need to build two LLVM backends and ship
them with rustc, every target we have now uses the same LLVM backend!

This removes the `src/llvm-emscripten` submodule and additionally
removes all support from rustbuild for building the emscripten LLVM
backend. Multiple codegen backend support is left in place for now, and
this is intended to be an easy 10-15 minute win on CI times by avoiding
having to build LLVM twice.

miri: add write_bytes method to Memory doing bounds-checks and supporting iterators

This lets us avoid some direct `Allocation` accesses in Miri.

…r=Centril

Remove unnecessary trait bounds and derivations

This PR removes unnecessary trait bounds and derivations from many types.

r? @nikomatsakis

…um,Centril

keep the root dir clean from debugging

We landed this before with rust-lang#63307 but recently in rust-lang#65630 the IMO bad ignore crept back in.

If you regularly do graphviz-based debugging and you are fine leaving junk in the rustc root dir, please configure your local `.git/info/exclude`. But most people working on rustc don't work with graphciz all that often (I for once never did), and not everyone likes to have stray generated files in their source dirs.

Also Cc rust-lang#63373 rust-lang#53768 @ecstatic-morse @Mark-Simulacrum

Fix typo from rust-lang#65214