I have this very simple program:

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    static constexpr const char *const str = "hello";
}

which fails to compile with this error:

$ gcc -std=c2x str.c
str.c: In function 'main':
str.c:6:46: error: 'constexpr' pointer initializer is not null
    6 |     static constexpr const char *const str = "hello";
      |                                              ^~~~~~~

$ gcc -v
...
gcc version 13.1.0 (MinGW-W64 x86_64-ucrt-posix-seh, built by Brecht Sanders)

Why is nullptr the only pointer type allowed to be constexpr?