`--emit=metadata` appears to override `--out-dir` if the latter is supplied first

[abonander]

See #40542

Explicitly adding --out-dir=$(TMPDIR) (supposedly redundant) after --emit=metadata appeared to fix the problem, suggesting that --emit=metadata overwrites --out-dir (which is included in $(RUSTC)) with the current directory (?).

This may not depend on the exact value of --emit; Cargo always appears to write --out-dir after --emit, so that might explain why this hasn't really come up before.

[steveklabnik]

Triage: I'm pretty sure that I know how to do this, but any chance you could add exact steps to reproduce here, @abonander ?

[Enselic]

Triage: I'll go ahead and close this as I think it is reasonable to require bug reports like these to have step-by-step instructions on how to reproduce. Of course feel free to re-open after providing reproduction steps!