Auto merge of #140154 - Berrysoft:cygwin-host, r=jieyouxu

Cygwin support in rustc

This PR builds host rustc targeting cygwin.

- [x] rust-lang/stacker#122
- [x] nagisa/rust_libloading#173
- [x] Detegr/rust-ctrlc#131
- [x] rust-random/getrandom#654
- [x] msys2/MSYS2-packages#5350
- [x] rust-lang/rust#140886
- [x] rust-lang/rust#140921
- [x] rust-lang/rust#140973

Currently supported:
* rustc
* rustdoc
* rustfmt
* clippy

Blocking:
* cargo: blocked by rust-lang/socket2#568
* rust-analyzer: needs `cargo update`, fixed upstream

```
$ rustc --version --verbose
rustc 1.88.0-dev
binary: rustc
commit-hash: unknown
commit-date: unknown
host: x86_64-pc-cygwin
release: 1.88.0-dev
LLVM version: 20.1.4
```

Author: bors