glr2.cc: fix GCC10 warning

For instance on test 433: "glr2.cc api.value.type={double}"

    tests/types.at:138: $CXX $CXXFLAGS $CPPFLAGS  $LDFLAGS -o test test.cc $LIBS
    stderr:
    In file included from /opt/local/include/gcc10/c++/bits/stl_tempbuf.h:60,
                     from /opt/local/include/gcc10/c++/bits/stl_algo.h:62,
                     from /opt/local/include/gcc10/c++/algorithm:62,
                     from test.cc:82:
    /opt/local/include/gcc10/c++/bits/stl_construct.h: In instantiation of 'constexpr decltype (::new(void*(0)) _Tp) std::construct_at(_Tp*, _Args&& ...) [with _Tp = glr_stack_item; _Args = {glr_stack_item}; decltype (::new(void*(0)) _Tp) = glr_stack_item*]':
    /opt/local/include/gcc10/c++/bits/alloc_traits.h:514:21:   required from 'static constexpr void std::allocator_traits<std::allocator<_CharT> >::construct(std::allocator_traits<std::allocator<_CharT> >::allocator_type&, _Up*, _Args&& ...) [with _Up = glr_stack_item; _Args = {glr_stack_item}; _Tp = glr_stack_item; std::allocator_traits<std::allocator<_CharT> >::allocator_type = std::allocator<glr_stack_item>]'
    /opt/local/include/gcc10/c++/bits/vector.tcc:115:30:   required from 'std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::emplace_back(_Args&& ...) [with _Args = {glr_stack_item}; _Tp = glr_stack_item; _Alloc = std::allocator<glr_stack_item>; std::vector<_Tp, _Alloc>::reference = glr_stack_item&]'
    /opt/local/include/gcc10/c++/bits/stl_vector.h:1204:21:   required from 'void std::vector<_Tp, _Alloc>::push_back(std::vector<_Tp, _Alloc>::value_type&&) [with _Tp = glr_stack_item; _Alloc = std::allocator<glr_stack_item>; std::vector<_Tp, _Alloc>::value_type = glr_stack_item]'
    test.cc:1949:48:   required from here
    /opt/local/include/gcc10/c++/bits/stl_construct.h:95:14: error: noexcept-expression evaluates to 'false' because of a call to 'glr_stack_item::glr_stack_item(const glr_stack_item&)' [-Werror=noexcept]
       95 |     noexcept(noexcept(::new((void*)0) _Tp(std::declval<_Args>()...)))
          |              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    test.cc:1436:3: note: but 'glr_stack_item::glr_stack_item(const glr_stack_item&)' does not throw; perhaps it should be declared 'noexcept'
     1436 |   glr_stack_item(const glr_stack_item& other)
          |   ^~~~~~~~~~~~~~
    cc1plus: all warnings being treated as errors
    stdout:
    tests/types.at:138: exit code was 1, expected 0
    433. types.at:138: 433. glr2.cc api.value.type={double} (types.at:138): FAILED (types.at:138)

* data/skeletons/glr2.cc (glr_stack_item): Use YY_NOEXCEPT/YY_NOTHROW.

data/skeletons/glr2.cc

@@ -1227,7 +1227,7 @@ class glr_stack_item {
       }
   }
 
-  glr_stack_item(const glr_stack_item& other)
+  glr_stack_item(const glr_stack_item& other) YY_NOEXCEPT YY_NOTHROW
     : isState_(other.isState_) {
     std::memcpy(raw_, other.raw_, union_size);
   }