py/compile: Raise SyntaxError if positional args are given after */**.

In CPython 3.4 this raises a SyntaxError.  In CPython 3.5+ having a
positional after * is allowed but uPy has the wrong semantics and passes
the arguments in the incorrect order.  To prevent incorrect use of a
function going unnoticed it is important to raise the SyntaxError in uPy,
until the behaviour is fixed to follow CPython 3.5+.

py/compile.c

@@ -2308,6 +2308,10 @@ STATIC void compile_trailer_paren_helper(compiler_t *comp, mp_parse_node_t pn_ar
             }
         } else {
             normal_argument:
+            if (star_flags) {
+                compile_syntax_error(comp, args[i], "non-keyword arg after */**");
+                return;
+            }
             if (n_keyword > 0) {
                 compile_syntax_error(comp, args[i], "non-keyword arg after keyword arg");
                 return;