[Bug c++/115471] New: Fail to capture (with initializer) constant bit-fields by reference in lambda expression

["fchelnokov at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115471

            Bug ID: 115471
           Summary: Fail to capture (with initializer) constant bit-fields
                    by reference in lambda expression
           Product: gcc
           Version: 14.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fchelnokov at gmail dot com
  Target Milestone: ---

This program
```
struct U {
    int i : 4;
};

using CU = const U;

auto lm = [&y = CU{5}.i]() { return y; };
```
is accepted by Clang and MSVC, and it shall be because when initializing a
const reference from a bit-field, a temporary is created (its type is the type
of the bit-field), copy initialized with the value of the bit-field, and the
reference is bound to that temporary.

But GCC fails here with the
error: cannot capture 'CU{5}.U::i' by reference

Online demo: https://gcc.godbolt.org/z/qnToW4qfY

Related discussion: https://stackoverflow.com/q/78611419/7325599