Braced init of complex type with different complex type not handled same as in Clang

[Vexu]

const _Complex double a = {1, 2};
const _Complex float b = {a};
_Static_assert(__imag b == 2, ""); // fails because the imaginary part is left default initialized to 0
const _Complex float c = {a, 4};
_Static_assert(__imag c == 4, "");