add a -Z no-index-update for crater and benchmarking

[Eh2406]

This is a fix for #3479

[rust-highfive]

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[alexcrichton]

Thanks! Could you be sure to add a test for this as well?

[alexcrichton]

@bors: r+

[bors]

📌 Commit ba05437 has been approved by alexcrichton

[bors]

⌛ Testing commit ba05437 with merge df11070...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: alexcrichton
Pushing df11070 to master...