Specialize to prototype for non-monomorphic functions.

Solves the trace-explosion problem with closure-heavy programming.

src/lj_parse.c

@@ -1392,7 +1392,7 @@ static GCproto *fs_finish(LexState *ls, BCLine line)
   pt->gct = ~LJ_TPROTO;
   pt->sizept = (MSize)sizept;
   pt->trace = 0;
-  pt->flags = fs->flags;
+  pt->flags = (uint8_t)(fs->flags & ~(PROTO_HAS_RETURN|PROTO_FIXUP_RETURN));
   pt->numparams = fs->numparams;
   pt->framesize = fs->framesize;
   setgcref(pt->chunkname, obj2gco(ls->chunkname));