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.
You still can't test for the existence of functions, non-macro constants, typedefs, structure members, or other arbitrary interfaces. Newer compiler introspection facilities like __has_include or __has_builtin generally only help with compiler portability.
musl libc specifically recommends using external feature detection a la autoconf, and is so opinionated about this that it refuses to add any identifying macros, like __GLIBC__.
that's a bygone practice from before compilers were widely capable.