This appears to have been broken by rust-lang/rust#76295

Steps to reproduce:

1. Run rustup-toolchain-install-master 0f9f0b384a0a3c997c1ea8f838f5591f12f96633
2. Run cargo +0f9f0b384a0a3c997c1ea8f838f5591f12f96633 check from the collector/benchmarks/packed-simd directory
3. Note the following error:

error[E0635]: unknown feature `mmx_target_feature`
   --> src/lib.rs:212:5
    |
212 |     mmx_target_feature,
    |     ^^^^^^^^^^^^^^^^^^

This is currently causes issues with perf runs. No indication is being given that this job is failing - instead, it's just not showing up on https://perf.rust-lang.org at all.