Explicitly protect automatic macros from being redefined and undefined

All current automatic macros are named in a way that do not pass the
name check in validName(), but that's kinda implicit. Specifically
test for ME_AUTO along with ME_BUILTIN.

No functional change due to the implicit protection from the naming.

(cherry picked from commit b88f43b)

rpmio/macro.c

@@ -608,7 +608,7 @@ validName(MacroBuf mb, const char *name, size_t namelen, const char *action)
     }
 
     mep = findEntry(mb->mc, name, namelen, NULL);
-    if (mep && (*mep)->flags & ME_BUILTIN) {
+    if (mep && (*mep)->flags & (ME_BUILTIN|ME_AUTO)) {
 	mbErr(mb, 1, _("Macro %%%s is a built-in (%s)\n"), name, action);
 	goto exit;
     }