If compiled with rustc --target=armv7-unknown-linux-gnueabihf -C target-feature=+v7,+neon neon.rs on 1.65.0, this gives the "No neon?!" compile error, but on my current nightly (rustc 1.67.0-nightly (215e3cd21 2022-11-03)), the same command works as expected, switching between both +neon and -neon. For aarch64-unknown-linux-gnueabihf, it seems to work correctly on the stable compiler.
Is there documentation around when and why it's supposed to work? Silently failing like this is very annoying.
EDIT: with rustc 1.67.0-nightly (6284998a2 2022-11-12), I seem to have only the v7 flag forwarded through cargo +nightly doc, not the neon flag. I'm starting to go crazy.