Looks like this function changed upstream, so it needs to be adjusted
for when used by libstd.

Conditionals and loops now have unstable features, and `feature_err` has
its own error code. I think that `feature_err` should take an error code
as a parameter, but don't have the energy to make this change throughout
the codebase. Also, the error code system may be torn out entirely.

Co-Authored-By: Mazdak Farrokhzad <[email protected]>

Co-Authored-By: Mazdak Farrokhzad <[email protected]>

doc comments: Less attribute mimicking

Make sure doc comments are not converted into intermediate meta-items, or not mixed with `doc(inline)` or something like that.

Follow-up to rust-lang#65750.

Enable `loop` and `while` in constants behind a feature flag

This PR is an initial implementation of rust-lang#52000. It adds a `const_loop` feature gate, which allows `while` and `loop` expressions through both HIR and MIR const-checkers if enabled. `for` expressions remain forbidden by the HIR const-checker, since they desugar to a call to `IntoIterator::into_iter`, which will be rejected anyways.

`while` loops also require [`#![feature(const_if_match)]`](rust-lang#66507), since they have a conditional built into them. The diagnostics from the HIR const checker will suggest this to the user.

r? @oli-obk
cc @rust-lang/wg-const-eval

…ly, r=alexcrichton

Remove i686-unknown-dragonfly target

DragonFly BSD removed support for i386 a while ago. It only supports x86_64 right now.

…lan-DPC

Fix signature of `__wasilibc_find_relpath`

Looks like this function changed upstream, so it needs to be adjusted
for when used by libstd.

Fix example code of OpenOptions::open

The example didn't set the access mode flag, which resulted in an `Err(InvalidInput)`.

r? @steveklabnik