Remove warning "suggest braces" for aggregate initialization of an empty class...

Remove warning "suggest braces" for aggregate initialization of an empty class with an aggregate base class.

I recently ran into issues with aggregates and inheritance, I'm using
it for creating a type-safe library where most of the types are build
over "tagged" std::array. After bit of cleaning and enabling -Wall
-Wextra -pedantic I noticed clang only in my pipeline gives me warning.
After a bit of focusing on it I found it's not helpful, and contemplate
disabling the warning all together. After a discussion with other
library authors I found it's bothering more people and decided to fix
it.

Removes this warning:

template<typename T, int N> struct StdArray {
    T contents[N];
  };

template<typename T, int N> struct AggregateAndEmpty : StdArray<T,N> { };

AggregateAndEmpty<int, 3> p = {1, 2, 3}; // <-- warning here about omitted braces