Issue #27961: Define HAVE_LONG_LONG as 1.

Fix backward compatibility issue, HAVE_LONG_LONG was defined but empty, whereas
it is defined as 1 in Python 3.5.

Author: vstinner

Include/pyport.h

@@ -39,7 +39,7 @@ Used in:  Py_SAFE_DOWNCAST
 
 // long long is required. Ensure HAVE_LONG_LONG is defined for compatibility.
 #ifndef HAVE_LONG_LONG
-#define HAVE_LONG_LONG
+#define HAVE_LONG_LONG 1
 #endif
 #ifndef PY_LONG_LONG
 #define PY_LONG_LONG long long