BUG: Avoid compilation error of wrapper file generated with SWIG >= 4.4 (numpy#30128)

The `import_array` macro, which is defined in the file
`numpy/core/code_generators/generate_numpy_api.py`, is intended for use
inside an internal SWIG function that is called in the generated C wrapper
file. This macro contains a return statement whose argument must match the
function definition.

Until version 4.3 of SWIG, the aforementioned function returned a `void*` value.
However, in version 4.4, the return value was changed to `int`. This causes compilation of code using import_array() to fail with the following error message: `returning 'void *' from a function with return type 'int' makes integer from pointer without a cast [-Wint-conversion].`

This commit resolves the issue by returning either `NULL` or `0`, depending
on the SWIG version being used (< 3.4 or >= 3.4, respectively). This change
has been successfully tested against SWIG versions 4.3 and 4.4.

Closes: numpy#30122

Author: rlaboiss

numpy/_core/code_generators/generate_numpy_api.py

@@ -157,14 +157,20 @@
   return 0;
 }
 
+#if (SWIG_VERSION < 0x040400)
+#define _RETURN_VALUE NULL
+#else
+#define _RETURN_VALUE 0
+#endif
+
 #define import_array() { \
   if (_import_array() < 0) { \
     PyErr_Print(); \
     PyErr_SetString( \
         PyExc_ImportError, \
         "numpy._core.multiarray failed to import" \
     ); \
-    return NULL; \
+    return _RETURN_VALUE; \
   } \
 }