'luaD_seterrorobj' should not raise errors

This function can be called unprotected, so it should not raise any
kind of errors. (It could raise a memory-allocation error when creating
a message).

ldo.h

@@ -67,6 +67,7 @@
 /* type of protected functions, to be ran by 'runprotected' */
 typedef void (*Pfunc) (lua_State *L, void *ud);
 
+LUAI_FUNC l_noret luaD_errerr (lua_State *L);
 LUAI_FUNC void luaD_seterrorobj (lua_State *L, TStatus errcode, StkId oldtop);
 LUAI_FUNC TStatus luaD_protectedparser (lua_State *L, ZIO *z,
                                                   const char *name,