Why do gcc and clang allow me to construct an abstract class?

The following code compiles on a wide range of gcc and clang versions - when compiled and run with gcc 5.3.1, it prints

A()

then aborts with a pure virtual call error.

#include <stdio.h>

class A
{
public:
    A() {
        printf("A()\n");
    }
    virtual void b() const = 0;
};

int main()
{
    const A& a{};
    a.b();
    return 0;
}

I realise binding a reference to a temporary is not ideal (though I think this case is covered by some sort of lifetime extension) - but it also works when trying to call a method that takes a const reference like:

Foo({});

For convenience, assuming links from new users are not banned, here's an example of it compiling with clang 3.2: Compiler Explorer