Adjust macros and typedefs for Numpy C API

- Define `Py_LIMITED_API` and `NPY_TARGET_VERSION` macros in
  setup.py rather than in the C source code.
- Don't define Numpy's `struct _typeobject` if we are building for
  PyPy because PyPy doesn't implement Python's limited C API
  (see liberfa/pyerfa#120).
- Define `struct _typeobject` workaround after including Python.h,
  not before, because on PyPy, Python.h defines the macros that we
  depend on to detect whether we are building under PyPy.
- Use `NPY_TARGET_VERSION` for builds that are backwards-compatible
  with old versions of Numpy.
- Build with any version of Numpy >=1.25 and <2
  (see liberfa/pyerfa#121).

pyproject.toml

@@ -4,6 +4,6 @@ requires = ["setuptools>=42.0.0",
             "setuptools_scm",
             "wheel",
             "extension-helpers",
-            "numpy>=1.25"]
+            "numpy>=1.25,<2"]
 
 build-backend = 'setuptools.build_meta'

setup.py

@@ -34,6 +34,9 @@ def get_extensions():
         'define_macros': [
             ('GSL_RANGE_CHECK_OFF', None),
             ('HAVE_INLINE', None),
+            ('Py_LIMITED_API', 0x03090000),
+            ('NPY_TARGET_VERSION', 'NPY_1_19_API_VERSION'),
+            ('NPY_NO_DEPRECATED_API', 'NPY_1_19_API_VERSION'),
         ],
         'extra_compile_args': [
             '-std=gnu11',

src/core.c

@@ -15,25 +15,6 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
-#define NPY_NO_DEPRECATED_API NPY_1_19_API_VERSION
-#define Py_LIMITED_API 0x03090000
-
-/* FIXME:
- * The Numpy C-API defines PyArrayDescr_Type as:
- *
- *   #define PyArrayDescr_Type (*(PyTypeObject *)PyArray_API[3])
- *
- * and then in some places we need to take its address, &PyArrayDescr_Type.
- * This is fine in GCC 10 and Clang, but earlier versions of GCC complain:
- *
- *   error: dereferencing pointer to incomplete type 'PyTypeObject'
- *   {aka 'struct _typeobject'}
- *
- * As a workaround, provide a faux forward declaration for PyTypeObject.
- * See https://github.com/numpy/numpy/issues/16970.
- */
-struct _typeobject {};
-
 #ifdef _OPENMP
 #include <omp.h>
 #endif
@@ -56,6 +37,24 @@ WARNINGS_POP
 #include "cubic_interp.h"
 #include "omp_interruptible.h"
 
+/* FIXME:
+ * The Numpy C-API defines PyArrayDescr_Type as:
+ *
+ *   #define PyArrayDescr_Type (*(PyTypeObject *)PyArray_API[3])
+ *
+ * and then in some places we need to take its address, &PyArrayDescr_Type.
+ * This is fine in GCC 10 and Clang, but earlier versions of GCC complain:
+ *
+ *   error: dereferencing pointer to incomplete type 'PyTypeObject'
+ *   {aka 'struct _typeobject'}
+ *
+ * As a workaround, provide a faux forward declaration for PyTypeObject.
+ * See https://github.com/numpy/numpy/issues/16970.
+ */
+#ifndef PYPY_VERSION
+struct _typeobject {};
+#endif
+
 
 static PyObject *
 get_num_threads(PyObject *NPY_UNUSED(module), void *NPY_UNUSED(args))