Broken build on macOS (Universal / Intel): cpuid instruction not available

Hello!

We have been investigating recent build failures of the master branch.
Currently both Intel and Universal builds are broken on macOS.

We tested building on macOS 26.4.1 with Xcode 26.2 and on macOS 14.5.

Universal builds
============

Universal builds are broken since this commit:
16743db: Centralize detection of x86 CPU features

To reproduce:

export CFLAGS="-arch arm64 -arch x86_64"
./configure --without-icu
make

This results in an error "cpuid instruction not available"

Universal builds used to work; they are broken since commit 16743db.

Intel Builds
========

Intel-only builds (using Rosetta) are also broken in master since the following commit:
5e13b0f: Use AVX2 for calculating page checksums where available

To reproduce:

arch -x86_64 zsh
./configure --without-icu
make

This results in an error:
checksum.c:57:6: error: call to undeclared function 'x86_feature_available'

Best regards,
Jakob Egger and Tobias Bussmann