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.

tests/local.at

@@ -1362,8 +1362,10 @@ AT_CHECK(m4_join([ ],
 # otherwise pass "-c"; this is a hack.  The default SOURCES is OUTPUT
 # with trailing ".o" removed, and ".cc" appended.
 m4_define([AT_COMPILE_CXX],
-[AT_KEYWORDS(c++)
+[AT_KEYWORDS([c++])
 AT_SKIP_IF([[! $BISON_CXX_WORKS]])
+m4_ifdef([AT_GLR2_CC_IF],
+  [AT_GLR2_CC_IF([AT_SKIP_IF([[test x"$CXX11_CXXFLAGS" == x]])])])
 AT_CHECK(m4_join([ ],
                  [$CXX $CXXFLAGS $CPPFLAGS $3],
                  [m4_bmatch([$1], [[.]], [-c], [$LDFLAGS])],

tests/output.at

@@ -744,6 +744,7 @@ m4_popdef([AT_TEST])
 AT_SETUP([C++ Output File Prefix Mapping])
 
 # AT_TEST([PREFIX], [DIRECTIVES])
+# -------------------------------
 m4_pushdef([AT_TEST],
 [AT_BISON_OPTION_PUSHDEFS([%skeleton "lalr1.cc" %define api.namespace {$1} $2])
 AT_LOC_PUSHDEF([begin.line], [begin.column], [end.line], [end.column])