[libc++][test] `array/size_and_alignment.compile.pass.cpp` includes non-Standard `<__type_traits/datasizeof.h>`

[StephanTLavavej]

Found while using MSVC's STL with libc++'s test suite.

This libcxx/test/std/ test should be portable, but it's including a non-Standard header:

llvm-project/libcxx/test/std/containers/sequences/array/size_and_alignment.compile.pass.cpp

Line 25 in 86b3f85

#include <__type_traits/datasizeof.h>

I'm not sure if this test should be changed to be portable, or moved to the implementation-specific libcxx/test/libcxx/ given this comment:

llvm-project/libcxx/test/std/containers/sequences/array/size_and_alignment.compile.pass.cpp

Lines 14 to 15 in 86b3f85

	// Make sure std::array<T, N> has the correct object size and alignment.
	// This test is mostly meant to catch subtle ABI-breaking regressions.

[frederick-vs-ja]

IIUC this file is testing non-portable implementation details. But I think most tested properties are expected to be provided by all implementations.