Ill-formed if constexpr branch in vector_operator CTS test for sycl::vec<bool>

[uditagarwal97]

Description

We have the following in the vector_operator test for sycl::vec<bool>, where the discarded branch of if constexpr is ill-formed - it is trying to increment vec<bool> which is not allowed by the SPEC.

if constexpr (!std::is_same_v<bool, bool>) {
      for (int i = 0; i < 1; ++i) {
        resArr[i] = static_cast<bool>(1);
      }
      for (int i = 0; i < 1; ++i) {
        resArr2[i] = static_cast<bool>(1) + static_cast<bool>(1);
      }
      testVec1Copy = testVec1;
      resVec = testVec1Copy++; // <------------------- Error

C++ requires that Outside a template, a discarded statement is fully checked. if constexpr is not a substitute for the #if preprocessing directive: https://en.cppreference.com/w/cpp/language/if

Faulty CTS test: https://github.com/KhronosGroup/SYCL-CTS/blob/SYCL-2020/tests/vector_operators/generate_vector_operators.py#L212

[uditagarwal97]

@gmlueck FYI

[aelovikov-intel]

Looks like it might have been fixed by #870.