Rollup merge of #36384 - petrochenkov:derclone, r=alexcrichton

Improve shallow `Clone` deriving

`Copy` unions now support `#[derive(Clone)]`.
Less code is generated for `#[derive(Clone, Copy)]`.
+
Unions now support `#[derive(Eq)]`.
Less code is generated for `#[derive(Eq)]`.

---
Example of code reduction:
```
enum E {
	A { a: u8, b: u16 },
	B { c: [u8; 100] },
}
```
Before:
```
fn clone(&self) -> E {
    match (&*self,) {
        (&E::A { a: ref __self_0, b: ref __self_1 },) => {
            ::std::clone::assert_receiver_is_clone(&(*__self_0));
            ::std::clone::assert_receiver_is_clone(&(*__self_1));
            *self
        }
        (&E::B { c: ref __self_0 },) => {
            ::std::clone::assert_receiver_is_clone(&(*__self_0));
            *self
        }
    }
}
```
After:
```
fn clone(&self) -> E {
    {
        let _: ::std::clone::AssertParamIsClone<u8>;
        let _: ::std::clone::AssertParamIsClone<u16>;
        let _: ::std::clone::AssertParamIsClone<[u8; 100]>;
        *self
    }
}
```

All the matches are removed, bound assertions are more lightweight.
`let _: Checker<CheckMe>;`, unlike `checker(&check_me);`, doesn't have to be translated by rustc_trans and then inlined by LLVM, it doesn't even exist in MIR, this means faster compilation.

---
Union impls are generated like this:
```
union U {
	a: u8,
	b: u16,
	c: [u8; 100],
}
```
```
fn clone(&self) -> U {
    {
        let _: ::std::clone::AssertParamIsCopy<Self>;
        *self
    }
}
```

Fixes https://github.com/rust-lang/rust/issues/36043
cc @durka
r? @alexcrichton

0 files changed, 0 insertions, 0 deletions