message: Adjust some of the Optional tests to test constexpr support in a way compatible with Visual Studio 2017.
diff: @@ -283,9 +283,9 @@ TEST(Optional_ConstExpr)
  CHECK_EQUAL(1, d);
  // FIXME: Visual Studio 2015's constexpr support isn't sufficient to allow this to compile.
  #ifndef _WIN32
  - constexpr bool e{Optional<int>{1}};
  + constexpr bool e = bool(Optional<int>{1});
  CHECK_EQUAL(true, e);
  - constexpr bool f{Optional<int>{none}};
  + constexpr bool f = bool(Optional<int>{none});
  CHECK_EQUAL(false, f);
  #endif
  constexpr int g = b.value_or(1234);
  @@ -303,9 +303,9 @@ TEST(Optional_ReferenceConstExpr)
  CHECK_EQUAL(bool(c), true);
  constexpr int d = *c;
  CHECK_EQUAL(0, d);
  - constexpr bool e{Optional<const int&>{global_i}};
  + constexpr bool e = bool(Optional<const int&>{global_i});
  CHECK_EQUAL(true, e);
  - constexpr bool f{Optional<const int&>{none}};
  + constexpr bool f = bool(Optional<const int&>{none});
  CHECK_EQUAL(false, f);
  }
  #endif
  