[Bug c++/88337] Implement P1002R1, P1327R1, P1330R0, C++20 relaxations of constexpr restrictions.

[emsr at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88337

--- Comment #1 from emsr at gcc dot gnu.org ---
LOL, this compiles:

// P1330R0 - Changing the active member of a union inside constexpr
union Foo
{
  int i;
  float f;
};

constexpr int
use()
{
  Foo foo{};
  foo.i = 3;
  foo.f = 1.2f;

  return 1;
}