The same effect can be achieved by `-Cllvm-args=-disable-preinline`.

…felix

Fix too restrictive checks on Drop impls

Fixes rust-lang#34426. Fixes rust-lang#58311.

This PR completes and extends rust-lang#59497 (which has been inactive for a while now).
The problem generating both issues was that when checking that the `Predicate`s of the `Drop` impl are exactly the same as the ones of the struct definition, the check was essentially performed by a simple `==` operator, which was not handling correctly HRTBs and involved `Fn` types.

The implemented solution relies on the `relate` machinery to more correctly equate `Predicate`s, and on `anonymize_late_bound_regions` to handle HRTB in a more general way. As the `Relate` trait currently is implemented only for `TraitPredicate` and `ProjectionPredicate` (and as they were the ones generating problems), `relate` is used only for them while for other `Predicate`s the equality check is kept. I'm currently considering whether it would make sense to implement the `Relate` trait also for all other `Predicate`s to render the proposed solution more general.

 Refactor type & bounds parsing thoroughly

PR is based on rust-lang#67131 with first one from this PR being ` extract parse_ty_tuple_or_parens`.

Also fixes rust-lang#67146.

r? @estebank

…, r=varkor

Enable opting out of specific default LLVM arguments.

`rustc` by default adds a few arguments to LLVM (like `-mergefunc-use-aliases` for example). With this PR `rustc` will only emit these arguments if the same argument has not already been specified by the user via `-Cllvm-args`. This enables opting out of these defaults.

The PR also removes a PGO specific `-Z` flag the effect of which can also be easily achieved by `-Cllvm-args`.

Fixes rust-lang#64310.

…=Dylan-DPC

Cleanup err codes

r? @Dylan-DPC

…ts, r=dtolnay

Make ptr::slice_from_raw_parts a const fn available under a feature flag

A first step in the direction of rust-lang#67456 .
This makes `ptr::slice_from_raw_parts` and `ptr::slice_from_raw_parts_mut` available as a const fn under a feature flag.