Add missing compiler flags and fix warnings (#4889)

This makes the build fail on warnings. It caught two out-of-bounds reads
and a deprecation warning.

wpilibcExamples/src/main/cpp/examples/RomiReference/include/RobotContainer.h

@@ -51,7 +51,7 @@ class RobotContainer {
                         OnBoardIO::ChannelMode::INPUT};
 
   // Example button
-  frc2::Button m_onboardButtonA{
+  frc2::Trigger m_onboardButtonA{
       [this] { return m_onboardIO.GetButtonAPressed(); }};
 
   // Autonomous commands.