Add support for unit testing from GradleRIO for C++ projects (#1094)

In order for this to properly work, we need to remove the main code.
Then the test component will actually have the main in it.  Example tests will be added later.

wpilibcExamples/src/main/cpp/templates/commandbased/cpp/Robot.cpp

@@ -72,4 +72,6 @@ void Robot::TeleopPeriodic() { frc::Scheduler::GetInstance()->Run(); }
 
 void Robot::TestPeriodic() {}
 
+#ifndef RUNNING_FRC_TESTS
 int main() { return frc::StartRobot<Robot>(); }
+#endif

wpilibcExamples/src/main/cpp/templates/iterative/cpp/Robot.cpp

@@ -55,4 +55,6 @@ void Robot::TeleopPeriodic() {}
 
 void Robot::TestPeriodic() {}
 
+#ifndef RUNNING_FRC_TESTS
 int main() { return frc::StartRobot<Robot>(); }
+#endif

wpilibcExamples/src/main/cpp/templates/sample/cpp/Robot.cpp

@@ -87,4 +87,6 @@ void Robot::OperatorControl() {
  */
 void Robot::Test() {}
 
+#ifndef RUNNING_FRC_TESTS
 int main() { return frc::StartRobot<Robot>(); }
+#endif

wpilibcExamples/src/main/cpp/templates/timed/cpp/Robot.cpp

@@ -55,4 +55,6 @@ void Robot::TeleopPeriodic() {}
 
 void Robot::TestPeriodic() {}
 
+#ifndef RUNNING_FRC_TESTS
 int main() { return frc::StartRobot<Robot>(); }
+#endif