…ents, r=thomcc

Use getentropy when possible on all Apple platforms

As the current code comments say, `SecRandomCopyBytes` is very heavyweight (regardless of purpose) compared to just asking the kernel directly for bytes from its own CSPRNG. We were not previously making an attempt to use the more efficient `getentropy` call on other Apple targets, instead solely using it on macOS. As the function is available on newer versions of Apple's different OSes, this changes the random filling to always attempt it first everywhere, only falling back to the less ideal alternatives after. This also cleans up the multiple Apple `imp` blocks into one.

It also should give a perf improvement, even if its likely unnoticeably small.

Refed XCode header for `getentropy` in the SDK:
```h
int getentropy(void* buffer, size_t size) __OSX_AVAILABLE(10.12) __IOS_AVAILABLE(10.0) __TVOS_AVAILABLE(10.0) __WATCHOS_AVAILABLE(3.0);
```

r? `@thomcc`

…iaskrgr

Rollup of 8 pull requests

Successful merges:

 - rust-lang#100970 (Allow deriving multipart suggestions)
 - rust-lang#100984 (Reinstate preloading of some dll imports)
 - rust-lang#101011 (Use getentropy when possible on all Apple platforms)
 - rust-lang#101025 (Add tier-3 support for powerpc64 and riscv64 openbsd)
 - rust-lang#101049 (Remove span fatal from ast lowering)
 - rust-lang#101100 (Make call suggestions more general and more accurate)
 - rust-lang#101171 (Fix UB from misalignment and provenance widening in `std::sys::windows`)
 - rust-lang#101185 (Tweak `WellFormedLoc`s a bit)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

…omcc

Remove Apple RNG fallbacks and simplify implementation

Now that we have [higher Apple platform requirements](rust-lang#104385), the RNG code can be simplified a lot. Since `getentropy` still doesn't look to be usable outside macOS this implementation:
- Removes any macOS fallback paths and unconditionally links to `getentropy`
- Minimizes the implementation for everything else (iOS, watchOS, etc).

`CCRandomGenerateBytes` was added in iOS 8 which means that we can use it now. It and `SecRandomCopyBytes` have the exact same functionality, but the former has a simpler API and no longer requires libstd to link to `Security.framework` for one function. Its also available in all the other target's SDKs.

Why care about `getentropy` then though on macOS? Well, its still much more performant. Benchmarking shows it runs at ~2x the speed of `CCRandomGenerateBytes`, which makes sense since it directly pulls from the kernel vs going through its own generator etc.

Semi-related to a previous, but reverted, attempt at improving this logic in rust-lang#101011