These look more like configure snapshots for Zig's bundled Clang than full ports of build system.

The HAVE_/WITH_ defines are supposed to be dynamically probed to adapt to different toolchain environments, setting them manually like that[1][2][3] could only work well for specific targets and for specific versions.

[1] https://github.com/allyourcodebase/libxml2/blob/38fb69d375bc...

[2] https://github.com/allyourcodebase/rnnoise/blob/47db9c212d7e...

[3] https://github.com/allyourcodebase/wayland/blob/f992cd71e199...