Python: fixing build for Python 3.8.

Thanks to tonyafanasyev.
This is related to #331 issue on GitHub.

auto/modules/python

@@ -64,6 +64,10 @@ nxt_found=no
 
 if /bin/sh -c "$NXT_PYTHON_CONFIG --prefix" >> $NXT_AUTOCONF_ERR 2>&1; then
 
+    if ${NXT_PYTHON_CONFIG} --embed 2>/dev/null; then
+        NXT_PYTHON_CONFIG="${NXT_PYTHON_CONFIG} --embed"
+    fi
+
     NXT_PYTHON_INCLUDE=`${NXT_PYTHON_CONFIG} --includes`
     NXT_PYTHON_LIBS=`${NXT_PYTHON_CONFIG} --ldflags`
 

src/nxt_python_wsgi.c

@@ -179,6 +179,10 @@ static PyTypeObject nxt_py_input_type = {
 #if PY_MAJOR_VERSION == 3 && PY_MINOR_VERSION > 3
     0,                                  /* tp_finalize          */
 #endif
+#if PY_MAJOR_VERSION == 3 && PY_MINOR_VERSION >= 8
+    0,                                  /* tp_vectorcall        */
+    0,                                  /* tp_print             */
+#endif
 };