BLD: 3.6.1 ABI compat (#16066)

Author: chris-b1

pandas/_libs/src/compat_helper.h

@@ -17,8 +17,19 @@ The full license is in the LICENSE file, distributed with this software.
 PySlice_GetIndicesEx changes signature in PY3
 but 3.6.1 in particular changes the behavior of this function slightly
 https://bugs.python.org/issue27867
+
+
+In 3.6.1 PySlice_GetIndicesEx was changed to a macro
+inadvertently breaking ABI compat.  For now, undefing
+the macro, which restores compat.
+https://github.com/pandas-dev/pandas/issues/15961
+https://bugs.python.org/issue29943
 */
 
+#if PY_VERSION_HEX < 0x03070000 && defined(PySlice_GetIndicesEx)
+  #undef PySlice_GetIndicesEx
+#endif
+
 PANDAS_INLINE int slice_get_indices(PyObject *s,
                                     Py_ssize_t length,
                                     Py_ssize_t *start,