BLD: enable building NumPy with Meson

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>

1 files changed, 21 insertions, 0 deletions

diff --git a/numpy/_build_utils/gcc_build_bitness.py b/numpy/_build_utils/gcc_build_bitness.py
new file mode 100644
index 000000000..fcad237e9
--- /dev/null
+++ b/numpy/_build_utils/gcc_build_bitness.py
@@ -0,0 +1,21 @@
+#!python
+""" Detect bitness (32 or 64) of Mingw-w64 gcc build target on Windows.
+"""
+
+import re
+from subprocess import run, PIPE
+
+
+def main():
+    res = run(['gcc', '-v'], check=True, text=True, capture_output=True)
+    target = re.search(r'^Target: (.*)$', res.stderr, flags=re.M).groups()[0]
+    if target.startswith('i686'):
+        print('32')
+    elif target.startswith('x86_64'):
+        print('64')
+    else:
+        raise RuntimeError('Could not detect Mingw-w64 bitness')
+
+
+if __name__ == "__main__":
+    main()