Continue supporting -Z instrument-coverage for compatibility for now,
but show a deprecation warning for it.

Update uses and documentation to use the -C option.

Move the documentation from the unstable book to stable rustc
documentation.

llvm-tools-preview is still experimental, so document it as such, and
don't use it in the examples.

…VM versions

The instrument-coverage option is stable; the details of the profile
data format are not.

Recommend llvm-tools-preview as the preferred alternative to obtain a
compatible version of the LLVM tools, rather than finding LLVM tools
elsewhere.

Co-authored-by: Mark Rousskov <mark.simulacrum@gmail.com>

…tions

These options primarily exist to work around bugs, and those bugs have
largely been fixed. Avoid stabilizing them, so that we don't have to
support them indefinitely.

The following *-unwind ABIs are now supported:
- "C-unwind"
- "cdecl-unwind"
- "stdcall-unwind"
- "fastcall-unwind"
- "vectorcall-unwind"
- "thiscall-unwind"
- "aapcs-unwind"
- "win64-unwind"
- "sysv64-unwind"
- "system-unwind"

The "CI" environment var isn't universal (for example, I think Azure
uses TF_BUILD). However, we are mostly concerned with rust-lang/rust's
own CI which currently is GitHub Actions which does set "CI". And I
think most other providers use "CI" as well.

Prior to a change, it would only look at types in bounds. When it started looking for consts,
shadowing type variables with a const would cause an ICE, so now defer looking at consts only if
there are no types present.

…overage, r=wesleywiser

Stabilize `-Z instrument-coverage` as `-C instrument-coverage`

(Tracking issue for `instrument-coverage`: rust-lang#79121)

This PR stabilizes support for instrumentation-based code coverage, previously provided via the `-Z instrument-coverage` option. (Continue supporting `-Z instrument-coverage` for compatibility for now, but show a deprecation warning for it.)

Many, many people have tested this support, and there are numerous reports of it working as expected.

Move the documentation from the unstable book to stable rustc documentation. Update uses and documentation to use the `-C` option.

Addressing questions raised in the tracking issue:

> If/when stabilized, will the compiler flag be updated to -C instrument-coverage? (If so, the -Z variant could also be supported for some time, to ease migrations for existing users and scripts.)

This stabilization PR updates the option to `-C` and keeps the `-Z` variant to ease migration.

> The Rust coverage implementation depends on (and automatically turns on) -Z symbol-mangling-version=v0. Will stabilizing this feature depend on stabilizing v0 symbol-mangling first? If so, what is the current status and timeline?

This stabilization PR depends on rust-lang#90128 , which stabilizes `-C symbol-mangling-version=v0` (but does not change the default symbol-mangling-version).

> The Rust coverage implementation implements the latest version of LLVM's Coverage Mapping Format (version 4), which forces a dependency on LLVM 11 or later. A compiler error is generated if attempting to compile with coverage, and using an older version of LLVM.

Given that LLVM 13 has now been released, requiring LLVM 11 for coverage support seems like a reasonable requirement. If people don't have at least LLVM 11, nothing else breaks; they just can't use coverage support. Given that coverage support currently requires a nightly compiler and LLVM 11 or newer, allowing it on a stable compiler built with LLVM 11 or newer seems like an improvement.

The [tracking issue](rust-lang#79121) and the [issue label A-code-coverage](https://github.com/rust-lang/rust/labels/A-code-coverage) link to a few open issues related to `instrument-coverage`, but none of them seem like showstoppers. All of them seem like improvements and refinements we can make after stabilization.

The original `-Z instrument-coverage` support went through a compiler-team MCP at rust-lang/compiler-team#278 . Based on that, ```@pnkfelix``` suggested that this needed a stabilization PR and a compiler-team FCP.

Windows: Disable LLVM crash dialog boxes.

This disables the crash dialog box on Windows. When LLVM hits an assertion, it will open a dialog box with Abort/Retry/Ignore. This is annoying on CI because CI will just hang until it times out (which can take hours).

Instead of opening a dialog box, it will print a message like this:

```
Assertion failed: isa<X>(Val) && "cast<Ty>() argument of incompatible type!", file D:\Proj\rust\rust\src\llvm-project\llvm\include\llvm/Support/Casting.h, line 255
```

Closes rust-lang#92829

Add more *-unwind ABI variants

The following *-unwind ABIs are now supported:
- "C-unwind"
- "cdecl-unwind"
- "stdcall-unwind"
- "fastcall-unwind"
- "vectorcall-unwind"
- "thiscall-unwind"
- "aapcs-unwind"
- "win64-unwind"
- "sysv64-unwind"
- "system-unwind"

cc ```@rust-lang/wg-ffi-unwind```

Fix ret > 1 bound if shadowed by const

Prior to a change, it would only look at types in bounds. When it started looking for consts,
shadowing type variables with a const would cause an ICE, so now defer looking at consts only if
there are no types present.

cc ``@compiler-errors``
Should Fix rust-lang#93553