enrich error info when tries to dlopen Enzyme

related: rust-lang#145899 (comment)

print error from EnzymeWrapper::get_or_init(sysroot) as a note

r? @ZuseZ4

e.g.

1. when libEnzyme not found

```shell
$ rustc +stage1 -Z autodiff=Enable -C lto=fat src/main.rs
error: autodiff backend not found in the sysroot: failed to find a `libEnzyme-21` folder in the sysroot candidates:
       * /Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib
  |
  = note: it will be distributed via rustup in the future
```

2. when could not load libEnzyme successfully

```shell
rustc +stage1 -Z autodiff=Enable -C lto=fat src/main.rs
error: failed to load our autodiff backend: DlOpen { source: "dlopen(/Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib/rustlib/aarch64-apple-darwin/lib/libEnzyme-21.dylib, 0x0005): tried: \'/Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib/rustlib/aarch64-apple-darwin/lib/libEnzyme-21.dylib\' (slice is not valid mach-o file), \'/System/Volumes/Preboot/Cryptexes/OS/Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib/rustlib/aarch64-apple-darwin/lib/libEnzyme-21.dylib\' (no such file), \'/Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib/rustlib/aarch64-apple-darwin/lib/libEnzyme-21.dylib\' (slice is not valid mach-o file)" }
```

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Rollup of 5 pull requests

Successful merges:

 - #150696 (enrich error info when tries to dlopen Enzyme)
 - #150721 (Deprecated doc intra link)
 - #150747 (tests/ui/runtime/on-broken-pipe/with-rustc_main.rs: Not needed so remove)
 - #150761 (rustc book: fix grammar)
 - #150775 (Move issue-12660 to 'ui/cross-crate/ with a descriptive name)

r? @ghost

enrich error info when tries to dlopen Enzyme

Implementation for rust-lang#150733.

I marked this function as `#[must_use]` even though the other `AtomicPtr` constructors aren't. It's unclear to me why they aren't already marked as such, I opened a zulip thread asking about it: [#t-libs > Is there a reason AtomicPtr constructors aren't #&rust-lang#91;must_use&rust-lang#93;?](https://rust-lang.zulipchat.com/#narrow/channel/219381-t-libs/topic/Is.20there.20a.20reason.20AtomicPtr.20constructors.20aren't.20.23.5Bmust_use.5D.3F/with/566624261).

enrich error info when tries to dlopen Enzyme

related: rust-lang#145899 (comment)

print error from EnzymeWrapper::get_or_init(sysroot) as a note

r? @ZuseZ4

e.g.

1. when libEnzyme not found

```shell
$ rustc +stage1 -Z autodiff=Enable -C lto=fat src/main.rs
error: autodiff backend not found in the sysroot: failed to find a `libEnzyme-21` folder in the sysroot candidates:
       * /Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib
  |
  = note: it will be distributed via rustup in the future
```

2. when could not load libEnzyme successfully

```shell
rustc +stage1 -Z autodiff=Enable -C lto=fat src/main.rs
error: failed to load our autodiff backend: DlOpen { source: "dlopen(/Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib/rustlib/aarch64-apple-darwin/lib/libEnzyme-21.dylib, 0x0005): tried: \'/Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib/rustlib/aarch64-apple-darwin/lib/libEnzyme-21.dylib\' (slice is not valid mach-o file), \'/System/Volumes/Preboot/Cryptexes/OS/Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib/rustlib/aarch64-apple-darwin/lib/libEnzyme-21.dylib\' (no such file), \'/Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib/rustlib/aarch64-apple-darwin/lib/libEnzyme-21.dylib\' (slice is not valid mach-o file)" }
```

enrich error info when tries to dlopen Enzyme

[slice::element_offset](https://doc.rust-lang.org/std/primitive.slice.html#method.element_offset)

Partially stabilizes rust-lang#126769 (substr_range).

[FCP completed](rust-lang#126769 (comment))

The other methods are [stalled because of the new range types](rust-lang#126769 (comment)), but this method doesn't use ranges.

enrich error info when tries to dlopen Enzyme

related: rust-lang#145899 (comment)

print error from EnzymeWrapper::get_or_init(sysroot) as a note

r? @ZuseZ4

e.g.

1. when libEnzyme not found

```shell
$ rustc +stage1 -Z autodiff=Enable -C lto=fat src/main.rs
error: autodiff backend not found in the sysroot: failed to find a `libEnzyme-21` folder in the sysroot candidates:
       * /Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib
  |
  = note: it will be distributed via rustup in the future
```

2. when could not load libEnzyme successfully

```shell
rustc +stage1 -Z autodiff=Enable -C lto=fat src/main.rs
error: failed to load our autodiff backend: DlOpen { source: "dlopen(/Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib/rustlib/aarch64-apple-darwin/lib/libEnzyme-21.dylib, 0x0005): tried: \'/Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib/rustlib/aarch64-apple-darwin/lib/libEnzyme-21.dylib\' (slice is not valid mach-o file), \'/System/Volumes/Preboot/Cryptexes/OS/Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib/rustlib/aarch64-apple-darwin/lib/libEnzyme-21.dylib\' (no such file), \'/Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib/rustlib/aarch64-apple-darwin/lib/libEnzyme-21.dylib\' (slice is not valid mach-o file)" }
```

enrich error info when tries to dlopen Enzyme

related: rust-lang#145899 (comment)

print error from EnzymeWrapper::get_or_init(sysroot) as a note

r? @ZuseZ4

e.g.

1. when libEnzyme not found

```shell
$ rustc +stage1 -Z autodiff=Enable -C lto=fat src/main.rs
error: autodiff backend not found in the sysroot: failed to find a `libEnzyme-21` folder in the sysroot candidates:
       * /Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib
  |
  = note: it will be distributed via rustup in the future
```

2. when could not load libEnzyme successfully

```shell
rustc +stage1 -Z autodiff=Enable -C lto=fat src/main.rs
error: failed to load our autodiff backend: DlOpen { source: "dlopen(/Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib/rustlib/aarch64-apple-darwin/lib/libEnzyme-21.dylib, 0x0005): tried: \'/Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib/rustlib/aarch64-apple-darwin/lib/libEnzyme-21.dylib\' (slice is not valid mach-o file), \'/System/Volumes/Preboot/Cryptexes/OS/Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib/rustlib/aarch64-apple-darwin/lib/libEnzyme-21.dylib\' (no such file), \'/Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib/rustlib/aarch64-apple-darwin/lib/libEnzyme-21.dylib\' (slice is not valid mach-o file)" }
```

enrich error info when tries to dlopen Enzyme

In rust-lang#127273 I added a test and a FIXME comment pointing out how it does the wrong thing. In the next commit I fixed the problem but forgot to remove the FIXME comment, whoops.

Rollup of 6 pull requests

Successful merges:

 - #150675 (MGCA: Support tuple expressions as direct const arguments)
 - #150696 (enrich error info when tries to dlopen Enzyme)
 - #150747 (tests/ui/runtime/on-broken-pipe/with-rustc_main.rs: Not needed so remove)
 - #150757 (Fix `alloc_error_handler` signature mismatch)
 - #150777 (Stabilize `slice::element_offset`)
 - #150791 (Remove out of date FIXME comment.)

r? @ghost

Rollup merge of #150696 - rm-FIXME, r=ZuseZ4

enrich error info when tries to dlopen Enzyme

In #127273 I added a test and a FIXME comment pointing out how it does the wrong thing. In the next commit I fixed the problem but forgot to remove the FIXME comment, whoops.