Extend C++17 feature checks to require std::optional

Source/Checks/cm_cxx17_check.cpp

@@ -1,6 +1,7 @@
 #include <cstdio>
 #include <iterator>
 #include <memory>
+#include <optional>
 #include <unordered_map>
 
 #ifdef _MSC_VER
@@ -27,5 +28,7 @@ int main()
   IDispatchPtr disp(ptr);
 #endif
 
-  return *u + *ai + *(bi - 1) + (3 - static_cast<int>(ci));
+  std::optional<int> oi = 0;
+
+  return *u + *ai + *(bi - 1) + (3 - static_cast<int>(ci)) + oi.value();
 }

bootstrap

@@ -1146,6 +1146,20 @@ int check_cxx14()
 }
 #endif
 
+#if __cplusplus >= 201703L
+#include <optional>
+int check_cxx17()
+{
+  std::optional<int> oi = 0;
+  return oi.value();
+}
+#else
+int check_cxx17()
+{
+  return 0;
+}
+#endif
+
 class Class
 {
 public:
@@ -1156,7 +1170,7 @@ private:
 int main()
 {
   auto const c = std::unique_ptr<Class>(new Class);
-  std::cout << c->Get() << check_cxx14() << std::endl;
+  std::cout << c->Get() << check_cxx14() << check_cxx17() << std::endl;
   return 0;
 }
 ' > "${TMPFILE}.cxx"