Do not unconditionally succeed RUSTC_WRAPPER checks when run by build scripts

[Veykril]

rust-analyzer's RUSTC_WRAPPER unconditionally succeeds cargo check
invocations tripping up build scripts using cargo check to probe for
successful compilations. To prevent this from happening the RUSTC_WRAPPER
now checks if it's run from a build script by looking for the
CARGO_CFG_TARGET_ARCH env var that cargo sets only when running build
scripts.

[eminence]

I tested this on two workspaces that exhibit the problem reported with anyhow, and in both cases the issue is fixed (and no obvious regressions)

[Veykril]

Thank you for testing! There shouldn't be any regressions caused due to this (unless cargo sets this env var in other occasions which it shouldn't)
@bors r+

[bors]

📌 Commit 72ae308 has been approved by Veykril

It is now in the queue for this repository.

[bors]

⌛ Testing commit 72ae308 with merge 5941dec...

[bors]

☀️ Test successful - checks-actions
Approved by: Veykril
Pushing 5941dec to master...

[sdroege]

This seems to cause unnecessary rebuilds, it seems. Some crate that depends on anyhow here will always rebuild anyhow and some other crates every time I run cargo build after saving in vim/coc-rust-analyzer. That wasn't the case before.

[Veykril]

this is only invoked on startup for rust-analyzer, so this cannot have changed the behavior for when you save

[sdroege]

Hrm, then something else must've changed between this and last Monday's release. Sorry for the noise here then.

[Veykril]

The only recent relevant change I could think of is #12808, but that is 2 releases ago, not one

[msfjarvis]

This seems to cause unnecessary rebuilds, it seems. Some crate that depends on anyhow here will always rebuild anyhow and some other crates every time I run cargo build after saving in vim/coc-rust-analyzer. That wasn't the case before.

You might be hitting this issue.

[sdroege]

Thanks, that seems to have fixed this