Add patch for object workaround

recipe/meta.yaml

@@ -11,6 +11,7 @@ source:
   sha256: f482ef62a10e686303f38c66f08df17b9ddee5ad82219c23571ee80d76abeea3
   patches:
     - numpy-args.patch
+    - object-workaround.patch
 
 build:
   number: 0

recipe/object-workaround.patch

@@ -0,0 +1,30 @@
+diff --git a/astropy_healpix/_core.c b/astropy_healpix/_core.c
+index 0a7c955..39d0dab 100644
+--- a/astropy_healpix/_core.c
++++ b/astropy_healpix/_core.c
+@@ -1,23 +1,3 @@
+-/* 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.
+- *
+- * Drop this when supporting gcc < 10 becomes irrelevant.
+- */
+-struct _typeobject {
+-    int _placeholder;
+-};
+-
+ #include <Python.h>
+ #include <numpy/arrayobject.h>
+ #include <numpy/ufuncobject.h>
+-- 
+2.42.1