Replace usage of the seemingly CPython-internal Py_ISSPACE() macro by a...

Replace usage of the seemingly CPython-internal Py_ISSPACE() macro by a dedicated inline function to make it work in C++ (where Py_ISSPACE() fails to link).

Closes https://github.com/cython/cython/issues/4111
Closes https://github.com/cython/cython/pull/4112

Cython/Utility/ModuleSetupCode.c

@@ -784,10 +784,6 @@ static CYTHON_INLINE PyObject * __Pyx_PyDict_GetItemStrWithError(PyObject *dict,
   #define PyObject_Format(obj, fmt)  PyObject_CallMethod(obj, "__format__", "O", fmt)
 #endif
 
-#if CYTHON_COMPILING_IN_PYPY && !defined(Py_ISSPACE)
-  #define Py_ISSPACE(c)  Py_UNICODE_ISSPACE(c)
-#endif
-
 // ("..." % x)  must call PyNumber_Remainder() if x is a string subclass that implements "__rmod__()".
 #define __Pyx_PyString_FormatSafe(a, b)   ((unlikely((a) == Py_None || (PyString_Check(b) && !PyString_CheckExact(b)))) ? PyNumber_Remainder(a, b) : __Pyx_PyString_Format(a, b))
 #define __Pyx_PyUnicode_FormatSafe(a, b)  ((unlikely((a) == Py_None || (PyUnicode_Check(b) && !PyUnicode_CheckExact(b)))) ? PyNumber_Remainder(a, b) : PyUnicode_Format(a, b))

Cython/Utility/Optimize.c

@@ -897,6 +897,12 @@ parse_failure:
     return -1.0;
 }
 
+static CYTHON_INLINE int __Pyx__PyBytes_AsDouble_IsSpace(char ch) {
+    // see Py_ISSPACE() in CPython
+    // https://github.com/python/cpython/blob/master/Python/pyctype.c
+    return (ch == 0x20) | !((ch < 0x9) | (ch > 0xd));
+}
+
 static CYTHON_UNUSED double __Pyx__PyBytes_AsDouble(PyObject *obj, const char* start, Py_ssize_t length) {
     double value;
     Py_ssize_t i, digits;
@@ -904,9 +910,9 @@ static CYTHON_UNUSED double __Pyx__PyBytes_AsDouble(PyObject *obj, const char* s
     char *end;
 
     // strip spaces at start and end
-    while (Py_ISSPACE(*start))
+    while (__Pyx__PyBytes_AsDouble_IsSpace(*start))
         start++;
-    while (start < last - 1 && Py_ISSPACE(last[-1]))
+    while (start < last - 1 && __Pyx__PyBytes_AsDouble_IsSpace(last[-1]))
         last--;
     length = last - start;
     if (unlikely(length <= 0)) goto fallback;