`build-dir` legacy layout post stablization cleanup

[ranger-ross]

The new build-dir layout tracked in #15010 was stabilized in #16807. However, the stabilization route we decided to go was to keep the legacy layout with a temporary __CARGO_TEMPORARY_BUILD_DIR_NEW_LAYOUT_OPT_OUT env var to allow them to opt out to ease the transition.

This issue issue tracks the removal of the legacy build-dir layout, including the opt out, implementation, and legacy tests.
In the stabilziation pull request, we called out that the legacy build-dir layout would be removed 1 release cycle after the new layout stabilization.

Checklist

• Remove -Zbuild-dir-new-layout flag
• Remove legacy build-dir tests
• Move the #[derive(Default)] back for CliUnstable - Stabilize build-dir layout v2  #16807 (comment)
• Rename deps_output to dylibs_path Reduce library search path length in new build dir layout #17191 (comment)
• Remove nightly only from some of the build-dir tests:

  cargo/tests/testsuite/build.rs

  Line 6620 in 3efb1f4

  #[cargo_test(

[epage]

While #15010 is closed, we've not closed the issues we are assuming this fixes. I'm hesitant until we know for sure this isn't being reverted :)

The issues are:

• Shadowing binaries on Windows (Workspace binary artifacts are added to target/debug/deps on Windows #7919)
• Collisions between intermediate build artifacts (Output filename collision with dylib on windows release mode #8794, output filename collision with panic = "abort" #16673)
• Inconsistent use of -Cextra-filename (Consider changing hashing behavior for executables. #8332)
• Slow performance when intermediate artifacts accumulate (Presence of old builds can dramatically raise incremental build time, via deps dir size growth #16665)

[epage]

@ranger-ross #15010 mentions

Move the #[derive(Default)] back for CliUnstable — Stabilize build-dir layout v2 #16807 (comment)

Would that be better to track here?

[weihanglo]

Yes. I didn't realize that issue was closed.

[Functionhx]

I can work on this. I'll clean up the build-dir legacy layout code path post-stabilization.

[ranger-ross]

I can work on this. I'll clean up the build-dir legacy layout code path post-stabilization.

@Functionhx FYI, the stablization was reverted in #17187 due to some issues discovered in the new layout.
We will need to fix the issues and re-stabilize it before we can do the cleanup work

[Functionhx]

Thanks for the heads-up. That makes sense — I’ll hold off on the cleanup until the new layout is fixed and re-stabilized.

[epage]

Even once we re-stabilize, we will need to wait a set period of time before we do any of the work in this issue in case we want another easy revert.