Rollup merge of rust-lang#85590 - jam1garner:tool-bootstrap-su-fix, r…

…=Mark-Simulacrum

Fix bootstrap using host exe suffix for cargo

When attempting to cross compile rustc (for example, from Linux to Windows) and tell it to build cargo/tools, the following error occurs:

```
thread 'main' panicked at 'src.symlink_metadata() failed with No such file or directory (os error 2)', src/bootstrap/lib.rs:1196:24
```

Relevant part of stack trace:
<details>

```
   2: bootstrap::Build::copy
             at ./src/bootstrap/lib.rs:1196:24
   3: <bootstrap::tool::ToolBuild as bootstrap::builder::Step>::run
             at ./src/bootstrap/tool.rs:220:13
```
</details>

If I add `-vvv` (which seemed to be the recommended course for debugging a similar issue according to [zulip logs](https://zulip-archive.rust-lang.org/182449tcompilerhelp/19655failedtobootstrap.html)), it shows:

```
Copy ".../rust/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-pc-windows-gnu/release/cargo" to ".../rust/build/x86_64-unknown-linux-gnu/stage2-tools-bin/cargo"
```
and when taking a look at the contents of `build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-pc-windows-gnu/release` it contains `cargo.exe`, but no `cargo`.

I tried to study the surrounding code to make sure this was the intended behavior and while I can't be 100% certain, it does seem that using the exe suffix for the `compiler.host` target instead of the `target` target won't have the desired behavior when cross-compiling to/from Windows.

src/bootstrap/tool.rs

@@ -217,9 +217,8 @@ impl Step for ToolBuild {
  if tool == "tidy" {
  tool = "rust-tidy";
  }
- let cargo_out =
- builder.cargo_out(compiler, self.mode, target).join(exe(tool, compiler.host));
- let bin = builder.tools_dir(compiler).join(exe(tool, compiler.host));
+ let cargo_out = builder.cargo_out(compiler, self.mode, target).join(exe(tool, target));
+ let bin = builder.tools_dir(compiler).join(exe(tool, target));
  builder.copy(&cargo_out, &bin);
  Some(bin)
  }