Change default for RUSTUP_WINDOWS_PATH_ADD_BIN

[ehuss]

This changes the default for the RUSTUP_WINDOWS_PATH_ADD_BIN opt-in to fix the issue where adding the bin directory on windows was preventing recursive calls to programs like cargo from being able to use the rustup proxies.

There was a call for testing at https://internals.rust-lang.org/t/help-test-windows-behavior-between-rustup-and-cargo/20237 and https://users.rust-lang.org/t/help-test-windows-behavior-between-rustup-and-cargo/106145. AFAIK, there have not been any indications of anyone having problems.

Fixes #3036

[cwfitzgerald]

Just raising that this seems to have broken cargo-nextest (issue) whenever there are proc-macro crates in the test suite. I don't know the details involved or which end this should be fixed on, just wanted to make the issue visible here. It seems like the nextest people have a way to fix it on their end, and setting RUSTUP_WINDOWS_PATH_ADD_BIN=1 in env allows things to work in the mean time, so this is non-blocking.

[smoelius]

As an additional data point, Dylint is currently using RUSTUP_WINDOWS_PATH_ADD_BIN=1 to support Windows.

It may be that we could set PATH ourselves, but having this environment variable in rustup is at least a convenience.

[djc]

Can one of you open a new issue discussing what the use case here is and how/why we broke it?