[hal] Implement stub mockdata on RoboRIO (#2575)

This makes it much more user-friendly to use simulation classes without needing
to ifdef for C++ to avoid linker errors or be very careful about construction
to avoid runtime errors in Java.

hal/src/main/native/athena/mockdata/DriverStationData.cpp

@@ -0,0 +1,51 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2017-2020 FIRST. All Rights Reserved.                        */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "hal/simulation/DriverStationData.h"
+
+#include "hal/simulation/SimDataValue.h"
+
+extern "C" {
+void HALSIM_ResetDriverStationData(void) {}
+
+#define DEFINE_CAPI(TYPE, CAPINAME, RETURN)                                 \
+  HAL_SIMDATAVALUE_STUB_CAPI_NOINDEX(TYPE, HALSIM, DriverStation##CAPINAME, \
+                                     RETURN)
+
+DEFINE_CAPI(HAL_Bool, Enabled, false)
+DEFINE_CAPI(HAL_Bool, Autonomous, false)
+DEFINE_CAPI(HAL_Bool, Test, false)
+DEFINE_CAPI(HAL_Bool, EStop, false)
+DEFINE_CAPI(HAL_Bool, FmsAttached, false)
+DEFINE_CAPI(HAL_Bool, DsAttached, false)
+DEFINE_CAPI(HAL_AllianceStationID, AllianceStationId,
+            HAL_AllianceStationID_kRed1)
+DEFINE_CAPI(double, MatchTime, 0)
+
+void HALSIM_SetJoystickAxes(int32_t joystickNum, const HAL_JoystickAxes* axes) {
+}
+
+void HALSIM_SetJoystickPOVs(int32_t joystickNum, const HAL_JoystickPOVs* povs) {
+}
+
+void HALSIM_SetJoystickButtons(int32_t joystickNum,
+                               const HAL_JoystickButtons* buttons) {}
+
+void HALSIM_SetJoystickDescriptor(int32_t joystickNum,
+                                  const HAL_JoystickDescriptor* descriptor) {}
+
+void HALSIM_GetJoystickOutputs(int32_t joystickNum, int64_t* outputs,
+                               int32_t* leftRumble, int32_t* rightRumble) {}
+
+void HALSIM_SetMatchInfo(const HAL_MatchInfo* info) {}
+
+void HALSIM_NotifyDriverStationNewData(void) {}
+
+void HALSIM_RegisterDriverStationAllCallbacks(HAL_NotifyCallback callback,
+                                              void* param,
+                                              HAL_Bool initialNotify) {}
+}  // extern "C"