* make isnan, isinf, isfinite, signbit, nextafter aliases

* fixes from review

Co-authored-by: Sebastian Berg <sebastianb@nvidia.com>

BLD: revert function() -> #define for 3 npymath functions

BLD: enable building NumPy with Meson

[ci skip]

This enables building with NumPy on Linux and macOS. Windows support
should be complete to, but is untested as of now and may need a few
tweaks. This contains:
- A set of `meson.build` files and related code generation script
  tweaks, header templates, etc.
- One CI job on Linux
- Basic docs on using Meson to build NumPy (not yet integrated in the
  html docs, it's too early for that - this is for early adopters right
  now).

The build should be complete, with the major exception of SIMD support.
The full test suite passes. See gh-22546 for the tracking issue with
detailed notes on the plan for switching NumPy to Meson as its build
system.

Co-authored-by: Stefan van der Walt <stefanv@berkeley.edu>

Closes gh-22100

This was put in place for universal builds (the old kind, PPC/Intel),
and then extended for arm64 support. It was only needed when building
for two architectures in a single build.

We no longer support i386/PPC/universal, and for producing universal2
wheels for those users that want that, the way to do it is to
take a x86-64 wheel and an arm64 wheel and fuse those with the
`delocate-fuse` utility from `delocate`.

Hence this code is no longer needed.