Based on rust-lang#68692

This lint checks that all declarations for extern fns of the same name
are declared with the same types.

- Allow ClashingExternDecl for lint-dead-code-3
- Update test case for rust-lang#5791
- Update test case for rust-lang#1866
- Update extern-abi-from-macro test case

Miri's pointer_offset_inbounds implementation has been moved into
librustc_mir as ptr_offset_inbounds (to avoid breaking miri on a
nightly update). The comments have been slightly reworked to better
match `offset`'s external documentation about what causes UB.

The intrinsic implementations are taken directly from miri.

Signed-off-by: Joe Richey <joerichey@google.com>

Signed-off-by: Joe Richey <joerichey@google.com>

Signed-off-by: Joe Richey <joerichey@google.com>

Signed-off-by: Joe Richey <joerichey@google.com>

Signed-off-by: Joe Richey <joerichey@google.com>

This is tricky to get right if we want to avoid panicking or wrapping.

Signed-off-by: Joe Richey <joerichey@google.com>

The previous code paniced if offset_bytes == i64::MIN. This commit:
  - Properly computes the absoulte value to avoid this panic
  - Adds a test for this edge case

Signed-off-by: Joe Richey <joerichey@google.com>

…or packed borrows in unsafe fns

Detect type parameter that might require lifetime constraint.
Do not name `ReVar`s in expected/found output.
Reword text suggesting to check the lifetimes.

We now perform the correct checks even if the pointer size differs
between the host and target.

Signed-off-by: Joe Richey <joerichey@google.com>

Tweak impl signature mismatch errors involving `RegionKind::ReVar` lifetimes

Fix rust-lang#66406, fix rust-lang#72106.

```
error: `impl` item signature doesn't match `trait` item signature
  --> $DIR/trait-param-without-lifetime-constraint.rs:14:5
   |
LL |     fn get_relation(&self) -> To;
   |     ----------------------------- expected `fn(&Article) -> &ProofReader`
...
LL |     fn get_relation(&self) -> &ProofReader {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ found `fn(&Article) -> &ProofReader`
   |
   = note: expected `fn(&Article) -> &ProofReader`
              found `fn(&Article) -> &ProofReader`
help: the lifetime requirements from the `impl` do not correspond to the requirements in the `trait`
  --> $DIR/trait-param-without-lifetime-constraint.rs:10:31
   |
LL |     fn get_relation(&self) -> To;
   |                               ^^ consider borrowing this type parameter in the trait
```

r? @nikomatsakis

Add a lint to catch clashing `extern` fn declarations.

Closes rust-lang#69390.

Adds lint `clashing_extern_decl` to detect when, within a single crate, an extern function of the same name is declared with different types. Because two symbols of the same name cannot be resolved to two different functions at link time, and one function cannot possibly have two types, a clashing extern declaration is almost certainly a mistake.

This lint does not run between crates because a project may have dependencies which both rely on the same extern function, but declare it in a different (but valid) way. For example, they may both declare an opaque type for one or more of the arguments (which would end up distinct types), or use types that are valid conversions in the language the extern fn is defined in. In these cases, we can't say that the clashing declaration is incorrect.

r? @eddyb

impl From<[T; N]> for Box<[T]>

Based on rust-lang#68692

Make pointer offset methods/intrinsics const

Implements rust-lang#71499 using [the implementations from miri](https://github.com/rust-lang/miri/blob/52f5d202bdcfe8986f0615845f8d1647ab8a2c6a/src/shims/intrinsics.rs#L96-L112).

I added some tests what's allowed and what's UB. Let me know if any other cases should be added.

CC: @RalfJung @oli-obk

linker: Support `-static-pie` and `-static -shared`

This PR adds support for passing linker arguments for creating statically linked position-independent executables and "statically linked" shared libraries.

Therefore it incorporates the majority of rust-lang#70740 except for the linker rerun hack and actually flipping the "`static-pie` is supported" switch for musl targets.

…afe-fn, r=nikomatsakis

Implement RFC 2585: unsafe blocks in unsafe fn

Tracking issue: rust-lang#71668
r? @RalfJung cc @nikomatsakis

…chievink

borrowck `DefId` -> `LocalDefId`

Replaces some `DefId`s which must always be local with `LocalDefId` in `librustc_mir/borrowck`.

cc @marmeladema