[Clang][C++20] CTAD on aggregates fails with designated initializers

[duk-37]

template <int N>
struct A { int f1[N]; };

int main() {
    A a1{ {1} }; // compiles fine
    A a2{ .f1 = {1} }; // error: no viable constructor or deduction guide for deduction of template arguments of 'T'
}

MSVC errors here too, GCC works.

Compiler Explorer

[llvmbot]

@llvm/issue-subscribers-c-20

Author: duk (duk-37)

```cpp template <int N> struct A { int f1[N]; };

int main() {
A a1{ {1} }; // compiles fine
A a2{ .f1 = {1} }; // error: no viable constructor or deduction guide for deduction of template arguments of 'T'
}

MSVC errors here too, GCC works.
</details>

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: duk (duk-37)

```cpp template <int N> struct A { int f1[N]; };

int main() {
A a1{ {1} }; // compiles fine
A a2{ .f1 = {1} }; // error: no viable constructor or deduction guide for deduction of template arguments of 'T'
}

MSVC errors here too, GCC works.
</details>