glr2.cc: require C++11

Reported by Dagobert Michelsen.
https://lists.gnu.org/r/bug-bison/2021-08/msg00006.html

* m4/bison-cxx-std.m4 (_BISON_CXXSTD_98_snippet): We don't need
vector::data, it was only for glr2.cc, which is C++11 anyway.
(_BISON_CXXSTD_11_snippet): We need vector::data and std::swap on
arrays.
* m4/cxx.m4 (BISON_TEST_FOR_WORKING_CXX_COMPILER): We don't need
vector::data.
* tests/local.at (AT_COMPILE_CXX): Skip when glr2.cc and no support
for C++11.

m4/cxx.m4

@@ -28,17 +28,13 @@ AC_DEFUN([BISON_TEST_FOR_WORKING_CXX_COMPILER],
     AC_COMPILE_IFELSE(
       [AC_LANG_PROGRAM(
          [[
-          #include <cassert>
           #include <cstdlib>
           #include <iostream>
           #include <map>
           #include <string>
-          #include <vector>
           using namespace std;]],
          [[std::cerr << "";
           cout << "";
-          std::vector<int> ints;
-          assert(ints.data () == &ints[0]);
           typedef std::pair<unsigned, int> uipair;
           std::map<unsigned, int> m;
           std::map<unsigned, int>::iterator i;