Rollup merge of #80932 - jyn514:download-windows-llvm, r=Mark-Simulacrum

Allow downloading LLVM on Windows and MacOS

- Don't ignore packaging `llvm/lib/` for `rust-dev` when LLVM is linked
statically
- Add `link-type.txt` so bootstrap knows whether llvm was linked
  statically or dynamically
- Don't assume CI LLVM is linked dynamically in `bootstrap::config`
- Fall back to dynamic linking if `link-type.txt` doesn't exist
- Fix existing bug that split the output of `llvm-config` on lines, not spaces
- Only special case MacOS when dynamic linking. Static linking works fine.
- Enable building LLVM tests

  This works around the following llvm bug:

  ```
  llvm-config: error: component libraries and shared library

  llvm-config: error: missing: /home/joshua/rustc2/build/x86_64-unknown-linux-gnu/llvm/build/lib/libgtest.a
  llvm-config: error: missing: /home/joshua/rustc2/build/x86_64-unknown-linux-gnu/llvm/build/lib/libgtest_main.a
  llvm-config: error: missing: /home/joshua/rustc2/build/x86_64-unknown-linux-gnu/llvm/build/lib/libLLVMTestingSupport.a
  thread 'main' panicked at 'command did not execute successfully: "/home/joshua/rustc2/build/x86_64-unknown-linux-gnu/llvm/build/bin/llvm-config" "--libfiles"
  ```

  I'm not sure why llvm-config thinks these are required, but to avoid
  the error, this builds them anyway.

- Bump version of `download-ci-llvm-stamp`

  `src/llvm-project` hasn't changed, but the generated tarball has.

Fixes https://github.com/rust-lang/rust/issues/77084.

# Current Status

This works on both MacOS and Windows! :tada: :tada: Thanks to ```@nagisa,``` ```@halkcyon,``` ```@Lokathor,``` ```@jryans,``` and ```@poliorcetics``` for helping me test!

The `if-available` check now supports all tier 1 platforms. Although only x64 apple and x64 msvc have been tested, none of the changes here are Windows or Mac specific, and I expect this to work anywhere that LLVM artifacts are uploaded to CI (i.e. the `rust-dev` component exists).

## Windows

Note that if you have an old version of MSVC build tools you'll need to update them. VS Build Tools 2019 14.28 and later are known to work. With old tools, you may see an error like the following:

```
error LNK2001: unresolved external symbol __imp___std_init_once_complete
```

0 files changed, 0 insertions, 0 deletions