rust-lang#69148 has a proper fix, but it is too big to backport.
This change avoids the ICE by actually emitting an appropriate error. The
output will be duplicated in some cases, but that's better than the
avoidable ICE.

Closes rust-lang#69078

Given `T: IntoIterator`/`IntoParallelIterator`, `T::Item` is
unambiguous, so we don't need the explicit trait casting.

…ceholder-type, r=Centril

Backport only: avoid ICE on bad placeholder type

 rust-lang#69148 has a proper fix, but it is too big to backport.
This change avoids the ICE by actually emitting an appropriate error. The
output will be duplicated in some cases, but that's better than the
avoidable ICE.

r? @Centril

resolve: `lifetimes.rs` -> `late/lifetimes.rs`

Lifetime resolution should ideally be merged into the late resolution pass, at least for named lifetimes.
Let's move it closer to it for a start.

update llvm to silence gcc 9 warnings

Closes rust-lang#69078

clarify operator precedence

…lan-DPC

Clean up E0373 explanation

r? @Dylan-DPC

…k-Simulacrum

Simplify the signature of par_for_each_in

Given `T: IntoIterator`/`IntoParallelIterator`, `T::Item` is
unambiguous, so we don't need the explicit trait casting.

…ls, r=Centril

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