This reverts commit 56e115a.

This removes a cause of `unwrap` and code complexity.

This allows replacing

```
option_value = Some(build());
option_value.as_mut().unwrap()
```

with

```
option_value.insert(build())
```

or

```
option_value.insert_with(build)
```

It's also useful in contexts not requiring the mutability of the reference.

Here's a typical cache example:

```
let checked_cache = cache.as_ref().filter(|e| e.is_valid());
let content = match checked_cache {
	Some(e) => &e.content,
	None => {
	    cache = Some(compute_cache_entry());
	    // unwrap is OK because we just filled the option
	    &cache.as_ref().unwrap().content
	}
};
```

It can be changed into

```
let checked_cache = cache.as_ref().filter(|e| e.is_valid());
let content = match checked_cache {
	Some(e) => &e.content,
	None => &cache.insert_with(compute_cache_entry).content,
};
```

`option.insert` covers both needs anyway, `insert_with` is
redundant.

Code cleaning made according to suggestions in discussion
on PR ##77392 impacts insert, get_or_insert and get_or_insert_with.

Co-authored-by: Mara Bos <m-ou.se@m-ou.se>

Co-authored-by: Ivan Tham <pickfire@riseup.net>

An empty enum is similar to the never type `!`, rather than the unit type `()`.

add `insert` to `Option`

This removes a cause of `unwrap` and code complexity.

This allows replacing

```
option_value = Some(build());
option_value.as_mut().unwrap()
```

with

```
option_value.insert(build())
```

It's also useful in contexts not requiring the mutability of the reference.

Here's a typical cache example:

```
let checked_cache = cache.as_ref().filter(|e| e.is_valid());
let content = match checked_cache {
	Some(e) => &e.content,
	None => {
	    cache = Some(compute_cache_entry());
	    // unwrap is OK because we just filled the option
	    &cache.as_ref().unwrap().content
	}
};
```

It can be changed into

```
let checked_cache = cache.as_ref().filter(|e| e.is_valid());
let content = match checked_cache {
	Some(e) => &e.content,
	None => &cache.insert(compute_cache_entry()).content,
};
```

*(edited: I removed `insert_with`)*

…nas-schievink

Revert "Allow dynamic linking for iOS/tvOS targets."

This reverts PR #73516.

On macOS I compile static libs for iOS, automated using [cargo-mobile](https://github.com/BrainiumLLC/cargo-mobile), which has worked smoothly for the past 2 years. However, upon updating to Rust 1.46.0, I was no longer able to use Rust on iOS. I've bisected this to the PR referenced above.

For most projects tested, apps now immediately crash with a message like this:
```
dyld: Library not loaded: /Users/francesca/Projects/example/target/aarch64-apple-ios/debug/deps/libexample.dylib
  Referenced from: /private/var/containers/Bundle/Application/745912AF-A928-465C-B340-872BD1C9F368/example.app/example
  Reason: image not found
dyld: launch, loading dependent libraries
DYLD_LIBRARY_PATH=/usr/lib/system/introspection
DYLD_INSERT_LIBRARIES=/Developer/usr/lib/libBacktraceRecording.dylib:/Developer/usr/lib/libMainThreadChecker.dylib:/Developer/Library/PrivateFrameworks/DTDDISupport.framework/libViewDebuggerSupport.dylib:/Developer/Library/PrivateFrameworks/GPUTools.framework/libglInterpose.dylib:/usr/lib/libMTLCapture.dylib
```

This can be reproduced by using cargo-mobile to generate a winit example project, and then attempting to run it on an iOS device (`cargo mobile init && cargo apple open`).

In our projects that depend on DisplayLink, the build instead fails with a linker error:
```
= note: Undefined symbols for architecture arm64:
            "_CACurrentMediaTime", referenced from:
                display_link::ios::run_callback_ios10::hda81197ff46aedbd in libapp-4f0abc1d7684103f.rlib(app-4f0abc1d7684103f.40d4iro0yz1iy487.rcgu.o)
                display_link::ios::run_callback_pre_ios10::h91f085da19374320 in libapp-4f0abc1d7684103f.rlib(app-4f0abc1d7684103f.40d4iro0yz1iy487.rcgu.o)
          ld: symbol(s) not found for architecture arm64
```

After reverting the change to enable dynamic linking on iOS, everything works the same as it did on Rust 1.45.2 for me.

In the future, would it be possible for me to be pinged when iOS-related PRs are made? I work for a company that intends on using Rust on iOS in production, so I'd gladly provide testing.

cc @aspenluxxxy

Simplify assert terminator only if condition evaluates to expected value

improve const infer error

For type inference we probably have to be careful about subtyping and stuff but considering that subtyping shouldn't be relevant for constants I don't really see a reason why we may not want to reuse the const origin here.

r? @varkor

Add regression test for issue-77475

Closes #77475

Update description of Empty Enum for accuracy

An empty enum is similar to the never type `!`, rather than the unit type `()`.