Defaulted default union constructor incorrectly deleted

struct NT {
  NT(); // non-trivial constructor
};

union U {
  U() = default;
  NT x;
  int y = 0;  // default member initializer
};

$ clang++ -c union1.cc  -std=c++17
union1.cc:6:3: warning: explicitly defaulted default constructor is implicitly deleted [-Wdefaulted-function-deleted]
  U() = default;
  ^
union1.cc:7:6: note: default constructor of 'U' is implicitly deleted because variant field 'x' has a non-trivial default constructor
  NT x;
     ^
1 warning generated.

This seems to contravene 15.1.5:

15.1 Constructors [...]

A defaulted default constructor for class X is defined as deleted if:
- X is a union that has a variant member with a non-trivial default constructor and no variant member of X has a default member initializer,

[...]

This issue may be related to https://github.com/llvm/llvm-project/issues/56313.

llvm / llvm-project

Defaulted default union constructor incorrectly deleted #56814