PR rust-lang#95604 introduced a "synthetic object file to ensure all exported and
used symbols participate in the linking". One constraint on this file is
that for MIPS-based targets, its architecture-specific ELF flags must be
the same as all other object files passed to the linker. That's enforced
by LLD, here:
https://github.com/llvm/llvm-project/blob/llvmorg-16.0.6/lld/ELF/Arch/MipsArchTree.cpp#L77

The current approach to determining e_flags for 32-bit was implemented
in PR rust-lang#96930, which links to this issue that summarizes the problem well:
ayrtonm/psx-sdk-rs#9

> ... the temporary object file is created with an e_flags which is
> invalid for 32-bit MIPS targets. The main issue is that it omits the ABI
> bits (EF_MIPS_ABI_O32) which implies it uses the N64 ABI.

To enable the N32 MIPS ABI (which succeeded O32), this patch enables
setting the synthetic object's ABI based on the target "llvm-abiname"
field, if it's given; otherwise, the O32 ABI is assumed for 32-bit MIPS
targets.

More information about the N32 ABI can be found here:
https://web.archive.org/web/20160121005457/http://techpubs.sgi.com/library/manuals/2000/007-2816-005/pdf/007-2816-005.pdf

Add extern declarations and optional dependencies to fix build done
directly via `cargo build`.

 - Introduce an Opaque type for adding information that is still
   internal to the compiler.

…i-obk

Implement a few more rvalue translation to smir

Add the implementation for a few more RValue variants. For now, I simplified the stable version of `RValue::Ref` by removing the notion of Region.

r? `@oli-obk`

…n-paths, r=lcnr

Don't suggest `impl Trait` in path position

Fixes rust-lang#113264.

Support explicit 32-bit MIPS ABI for the synthetic object

PR rust-lang#95604 introduced a "synthetic object file to ensure all exported and used symbols participate in the linking". One constraint on this file is that for MIPS-based targets, its architecture-specific ELF flags must be the same as all other object files passed to the linker. That's enforced by LLD, here:
https://github.com/llvm/llvm-project/blob/llvmorg-16.0.6/lld/ELF/Arch/MipsArchTree.cpp#L77

The current approach to determining e_flags for 32-bit was implemented in PR rust-lang#96930, which links to this issue that summarizes the problem well: ayrtonm/psx-sdk-rs#9

> ... the temporary object file is created with an e_flags which is
> invalid for 32-bit MIPS targets. The main issue is that it omits the ABI
> bits (EF_MIPS_ABI_O32) which implies it uses the N64 ABI.

To enable the N32 MIPS ABI (which succeeded O32), this patch enables setting the synthetic object's ABI based on the target "llvm-abiname" field, if it's given; otherwise, the O32 ABI is assumed for 32-bit MIPS targets.

More information about the N32 ABI can be found here: https://web.archive.org/web/20160121005457/http://techpubs.sgi.com/library/manuals/2000/007-2816-005/pdf/007-2816-005.pdf

…-loc, r=compiler-errors

Lint against misplaced where-clauses on associated types in traits

Extends the scope of the lint `deprecated_where_clause_location` (rust-lang#89122) from associated types in impls to associated types in any location (impl or trait). This is only relevant for `#![feature(associated_type_defaults)]`. Previously we didn't warn on the following code for example:

```rs
#![feature(associated_type_defaults)]
trait Trait { type Assoc where u32: Copy = (); }
```

Personally I would've preferred to emit a *hard* error here instead of a lint warning since the feature is unstable but unfortunately we are constrained by back compat as associated type defaults won't necessarily trigger the feature-gate error if they are inside of a macro call (since they use a post-expansion feature-gate due to historical reasons, see also rust-lang#66004).

I've renamed and moved related preexisting tests: 1. They test AST validation passes not the parser & thus shouldn't live in `parser/` (historical reasons?). 2. One test file was named after type aliases even though it tests assoc tys.

`@rustbot` label A-lint