Fix bootstrap rust build failure for vxworks

[gautam899]

Fixes #153332

Starting with VxWorks 25.09, struct stat was updated to use struct timespec instead of time_t for timestamp fields.

The following changes were made in libc in the commit libc.

As a result, when performing a bootstrap build with VxWorks ≥ 25.09, libc no longer exposes the fields st_mtime, st_atime, and st_ctime, as they are conditionally compiled in src/vxworks/mod.rs here libc. This causes the build to fail.

For VxWorks versions earlier than 25.09, the build completes successfully without errors.

This PR resolves the issue by detecting the WIND_RELEASE_ID environment variable (which is set in the VxWorks build environment) and conditionally guarding the affected functions in the two additional files where the errors originate.

[rustbot]

r? @Mark-Simulacrum

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[gautam899]

ping @biabbas

[Mark-Simulacrum]

Can you add documentation for the environment variable to https://doc.rust-lang.org/nightly/rustc/platform-support/vxworks.html?

cc rust-lang/rfcs#3750 as well, which seems like the long term solution here

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.