Regression: cannot find proc-macro-srv only on Windows

rust-analyzer version: Anything since 0.3.1498. 0.3.1489 and earlier are unaffected

rustc version: reproduced with 1.67 and 1.75 on Windows. Could not reproduce with either on Linux

relevant settings: none

When cursor is moved over the sad rust-analyzer thing at the bottom in VS Code, you will see cannot find proc-macro-srv, the workspace C:\whatever is missing a sysroot. Repro should be as simple as

rustup default stable
cargo init

and open VS Code in this directory.

It's possible that installing rust-src fixes this. Our nostd-only Rust toolchain isn't shipped with sources so this isn't an option. Though we're interested in this bug because of our nostd-only toolchain, all behavior described above this paragraph applies to Windows stable as well.

I somewhat suspect that the VS Code and Windows changes by @Veykril may be the culprit based on looking at the output of git log --stat 2023-04-24..2023-05-01 --first-parent

Reproduce on Windows with rustup default stable, cargo init, and VS Code, comparing rust-analyzer 0.3.1489 with versions since 0.3.1498. Inspect the VS Code and Windows changes in git log --stat 2023-04-24..2023-05-01 --first-parent, and check behavior with and without rust-src. Done means proc-macro-srv is found for Windows stable and the missing-sysroot error no longer appears.