[Bug libstdc++/65631] New: seed_seq should not be copyable

["rs2740 at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65631

            Bug ID: 65631
           Summary: seed_seq should not be copyable
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rs2740 at gmail dot com

>From http://stackoverflow.com/q/29350040/2756719, repro:

#include <random>

int main(int, char **)
{
  std::seed_seq seed1{1337, 42};
  std::seed_seq seed2(seed1);
  std::seed_seq seed3 = seed2;
  return 0;
}

Per the class synopsis in [rand.util.seedseq], the copy constructor and
assignment operator of seed_seq are deleted:

// no copy functions
seed_seq(const seed_seq& ) = delete;
void operator=(const seed_seq& ) = delete;

But the above code, incorrectly, compiles using libstdc++.