g++ and clang++ different behaviour with lambda capturing `std::integral_constant` by reference

Given the following code

#include <type_traits>

int main ()
 {
   std::integral_constant<int, 42> ic;

   [&]{ constexpr int i = ic; (void)i; }();
 }

(the (void)i; is just to avoid a "unused variable" warning) clang++ compile without problem where g++ gives the following error

prog.cc: In lambda function:
prog.cc:7:27: error: '__closure' is not a constant expression
    7 |    [&]{ constexpr int i = ic; (void)i; }();
      |                           ^~

Capturing by value

[=]{ constexpr int i = ic; (void)i; }();

both compilers compile without problem.

The question, as usual, is: who's right? g++ or clang++?