Give errors for certain illegal initializers.

This prohibits initializers in "extern" declarations within a function, and in the parameter declarations of non-prototyped functions.

Here are examples illustrating these cases:

int main(void) {
        extern int i = 50;
}

void f(i)
int i = 60;
{
}

Parser.pas

@@ -4123,8 +4123,11 @@ else {if not isFunction then} begin
       Error(141);
    if token.kind = eqch then begin
       if declSpecifiers.storageClass = typedefsy then
-         Error(52);
-      if doingPrototypes then
+         Error(52)
+      else if declSpecifiers.storageClass = externsy then
+         if doingFunction then
+            Error(22);
+      if doingPrototypes or doingParameters then
          Error(88);
                                         {allocate copy of incomplete array type,}
       tp := variable^.itype;            {so it can be completed by Initializer}