…18530)

Pulled out of #18517

I don't have aarch64 hardware available locally, but Claude posited: 

> When an armv7 binary runs on an aarch64 kernel (e.g., armv7l
containers on aarch64 hosts, or 32-bit Raspberry Pi OS on 64-bit
hardware), /proc/cpuinfo reports aarch64-style feature flags instead of
armv7 flags. The existing check for "vfp" fails because aarch64 uses
"fp" instead.
> 
> Add detection of the aarch64 "fp" feature flag (mandatory on all
aarch64 CPUs) as a discrete token, indicating hardware floating-point
support. This ensures uv selects the gnueabihf (hard-float) Python
variant instead of the gnueabi (soft-float) variant.

I reproduced this in #18532

Under QEMU on aarch64 macOS, both the `vfp` and `fp` feature flags are
set.

Closes #18509