Add a test to ensure including a libcu++ header doesn't break gcc's immintrin.h

[jrhemstad]

As https://github.com/fwyzard/nvidia_bug_4139266 showed, including a libcu++ header was breaking gcc's immintrin.h header.

While it is extremely unlikely that this would happen again, it is simple enough for us to add a test to make sure it does not.

We should add a simple test like:

// UNSUPPORTED: !gcc
#include <cuda/std/type_traits>
#include <immintrin.h>

int main(){}