Be more conservative about is_trivial support

`std::is_trivial` is part of the C++14 specification. However, we have
encountered multiple compilers that purport to implement C++14 but do
not implement `std::is_trivial` and the like checks correctly.

To avoid such issues, only use `std::is_trivial` on compilers that we
have tested to support it.

vtkm/cont/testing/UnitTestMoveConstructors.cxx

@@ -23,6 +23,8 @@
 #include <vtkm/TypeList.h>
 #include <vtkm/cont/testing/Testing.h>
 
+#include <vtkmstd/is_trivial.h>
+
 #include <type_traits>
 
 namespace
@@ -63,7 +65,7 @@ template<typename T>
 void is_triv_noexcept_movable()
 {
   constexpr bool valid =
-#if !(defined(__GNUC__) && (__GNUC__ <= 5))
+#ifdef VTKM_USE_STD_IS_TRIVIAL
                          //GCC 4.X and compilers that act like it such as Intel 17.0
                          //don't have implementations for is_trivially_*
                          std::is_trivially_move_constructible<T>::value &&

vtkm/exec/internal/testing/UnitTestVariant.cxx

@@ -232,7 +232,7 @@ void TestIndexing()
 
 void TestTriviallyCopyable()
 {
-#ifndef VTKM_USING_GLIBCXX_4
+#ifdef VTKM_USE_STD_IS_TRIVIAL
   // Make sure base types are behaving as expected
   VTKM_STATIC_ASSERT(std::is_trivially_constructible<float>::value);
   VTKM_STATIC_ASSERT(std::is_trivially_copyable<float>::value);

vtkm/testing/UnitTestPair.cxx

@@ -13,6 +13,8 @@
 #include <vtkm/Types.h>
 #include <vtkm/VecTraits.h>
 
+#include <vtkmstd/is_trivial.h>
+
 #include <vtkm/testing/Testing.h>
 
 namespace
@@ -135,8 +137,11 @@ void PairTest()
 
     // Pair types should preserve the trivial properties of their components.
     // This insures that algorithms like std::copy will optimize fully.
-    VTKM_TEST_ASSERT(std::is_trivial<T>::value &&
-                       std::is_trivial<U>::value == std::is_trivial<P>::value,
+    // (Note, if std::is_trivial is not supported by the compiler, then
+    // vtkmstd::is_trivial will always report false, but VTKM_IS_TRIVIAL will
+    // always succeed.)
+    VTKM_IS_TRIVIAL(T);
+    VTKM_TEST_ASSERT(vtkmstd::is_trivial<U>::value == vtkmstd::is_trivial<P>::value,
                      "PairType's triviality differs from ComponentTypes.");
   }
 

vtkm/testing/UnitTestTypes.cxx

@@ -10,6 +10,8 @@
 
 #include <vtkm/Types.h>
 
+#include <vtkmstd/is_trivial.h>
+
 #include <vtkm/testing/Testing.h>
 
 namespace
@@ -315,7 +317,7 @@ void GeneralVecTypeTest(const vtkm::Vec<ComponentType, Size>&)
 
   // Vector types should preserve the trivial properties of their components.
   // This insures that algorithms like std::copy will optimize fully.
-  VTKM_TEST_ASSERT(std::is_trivial<ComponentType>::value == std::is_trivial<T>::value,
+  VTKM_TEST_ASSERT(vtkmstd::is_trivial<ComponentType>::value == vtkmstd::is_trivial<T>::value,
                    "VectorType's triviality differs from ComponentType.");
 
   VTKM_TEST_ASSERT(T::NUM_COMPONENTS == Size, "NUM_COMPONENTS is wrong size.");

vtkmstd/is_trivial.h

@@ -11,10 +11,17 @@
 #define vtk_m_std_is_trivial_h
 
 #include <vtkm/StaticAssert.h>
+#include <vtkm/internal/Configure.h>
 
 #include <type_traits>
 
-#if defined(VTKM_USING_GLIBCXX_4)
+#if defined(VTKM_GCC) && !defined(VTKM_USING_GLIBCXX_4)
+#define VTKM_USE_STD_IS_TRIVIAL
+#elif defined(VTKM_CLANG)
+#define VTKM_USE_STD_IS_TRIVIAL
+#endif
+
+#ifndef VTKM_USE_STD_IS_TRIVIAL
 namespace vtkmstd
 {