clang++: alias template ignores alignment given by `__attribute__((aligned(X)))`

[richardebeling]

This code:

#include <iostream>
#include <cstdint>

template <typename T=void>
using TemplatedT __attribute__((aligned(8))) = uint32_t;

using ManualT __attribute__((aligned(8))) = uint32_t;

int main() {
    std::cout << "alignof Template: " << alignof(TemplatedT<>) << std::endl;
    std::cout << "alignof Manual:   " << alignof(ManualT) << std::endl;
}

prints (godbolt)

alignof Template: 4
alignof Manual:   8

when compiled with clang (in the version currently available as "trunk" on godbolt).

I would have expected both types to have an alignment of 8. I've asked on StackOverflow, and the comments indicated this may be a bug, so I'm reporting this here.

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