Update .pro file and add test C++17 statements to main

The test statements are making sure C++17 features are enabled on all
compilers. They should not be pushed to master as they are.

src/main.cpp

@@ -348,6 +348,15 @@ int main( int argc, char* argv[] )
 {
     setUpLogging( argc, argv );
 
+    // Initializers in if statements is a C++17 feature. Should be removed after
+    // making sure CI works with this.
+    if ( constexpr int i = 2; i > 10 )
+    {
+        // static_assert with no message is a C++17 feature. Should be removed
+        // after making sure CI works with this.
+        static_assert( i < 5 );
+    }
+
     const bool desktopMode = argument::CheckCommandLineArgument(
         argc, argv, argument::kDesktopMode );
     const bool noSound