[SYCL][LIT] Check POD-ness for types crossing ABI boundary

[uditagarwal97]

Added test to check POD-ness of SYCL types when crossing ABI boundaries. POD-ness if changed outside the ABI breaking window, can break the ABI and cause undefined behavior.

[uditagarwal97]

This test is not exhaustive and I only considered types for which we already have abi layout tests.

[Copilot]

Pull request overview

This PR adds a LIT test to verify type traits (POD-ness, trivial copyability, standard layout) of SYCL types that cross ABI boundaries, ensuring these properties remain stable to prevent ABI breakage and undefined behavior.

Changes:

• Added comprehensive type trait verification test for 18 SYCL types commonly used across ABI boundaries
• Implemented test infrastructure using FileCheck to validate type properties remain consistent

[uditagarwal97]

I think I'd have to split this test for Linux and Windows... Some types are standard_layout for gcc but not for MSVC.

[againull]

I think we should change cout/FileCheck to static_assert checks, i.e. something like:

template <typename T, bool IsTriviallyCopyable,
            bool IsTriviallyDefaultConstructible,
            bool IsStandardLayout>
  void check_type_traits() {
    static_assert(std::is_trivially_copyable_v<T> == IsTriviallyCopyable,
                  "Trivially copyable trait changed");
...

It will also allow to easier differentiate between msvc/gcc if any differences:

  #ifdef ..
    check_type_traits<some_type, false, false, false>();  // MSVC
  #else
    check_type_traits<some_type, false, false, true>();   // GCC
  #endif