Reporitng libstdc++ bug without account to Bugzilla

[Palmu, Miro M]

Hi

I think I found libstdc++ bug and I tried to report to Bugzilla but "user 
account creation has been restricted".

So I'm going to report it here in hope that someone with a account could report 
it to Bugzilla if they seem it fit.

Using gcc 13.2 with -std=c++23 code below (https://godbolt.org/z/Kc36rcMYx) 
does not compile even if all compile time
allocations are freed before returning from compile time context. MSVC is able 
to compile it.

I was suggested elsewhere that it could be some oversight in the SSO 
implementation.
 
```
#include <string>
#include <functional>
#include <algorithm>
#include <vector>

using namespace std;
using namespace std::literals;

constexpr auto foo() {
    const auto vec = vector{ "a"s, "b"s, "c"s };
    return ranges::fold_left(vec, ""s, plus{});
}

constexpr auto bar() {
    return foo().size();
}

int main() {
    constexpr auto _ = bar(); // This does not compile
}
```

Error message:

```
<source>: In function 'int main()':
<source>:19:27:   in 'constexpr' expansion of 'bar()'
<source>:15:23:   in 'constexpr' expansion of 'foo()()'
<source>:19:28:   in 'constexpr' expansion of 
'std::ranges::__fold_left_fn::operator()(_Range&&, _Tp, _Fp) const [with _Range 
= const std::vector<std::__cxx11::basic_string<char>, 
std::allocator<std::__cxx11::basic_string<char> > >&; _Tp = 
std::__cxx11::basic_string<char>; _Fp = std::plus<void>](vec, 
std::literals::string_literals::operator""s(const char*, std::size_t)(0), 
(std::plus<void>(), std::plus<void>()))'
<source>:19:28:   in 'constexpr' expansion of 
'std::__cxx11::basic_string<char>((* & 
std::move<__cxx11::basic_string<char>&>(__init)))'
<source>:19:28: error: accessing 'std::__cxx11::basic_string<char>::<unnamed 
union>::_M_allocated_capacity' member instead of initialized 
'std::__cxx11::basic_string<char>::<unnamed union>::_M_local_buf' member in 
constant expression
   19 |     constexpr auto _ = bar();
      |                            ^
```

Miro Palmu