message: Clarification: Adds a comment about which compilers define `__GNUC__`
diff: #include "axom/core/Types.hpp"
  // Check for and setup defines for platform-specific intrinsics
  +// Note: `__GNUC__` is defined for the gnu, clang and intel compilers
  #if defined(_WIN64) && (_MSC_VER >= 1600)
  #define _AXOM_CORE_USE_INTRINSICS_MSVC
  #include <intrin.h>
  