Make FRCUsageReporting.h C-compatible (#2070)

Now that HAL_Report has been moved into FRCUsageReporting.h,
this should also be C-compatible.

This also removes the C++ ifdef guard in HAL.h.

hal/src/generate/FRCUsageReporting.h.in

@@ -42,6 +42,7 @@ int64_t HAL_Report(int32_t resource, int32_t instanceNumber, int32_t context,
  * Autogenerated file! Do not manually edit this file.
  */
 
+#ifdef __cplusplus
 namespace HALUsageReporting {
   typedef enum {
 ${usage_reporting_types_cpp}
@@ -50,3 +51,4 @@ ${usage_reporting_types_cpp}
 ${usage_reporting_instances_cpp}
   } tInstances;
 }
+#endif

hal/src/main/native/include/hal/HAL.h

@@ -24,6 +24,7 @@
 #include "hal/DriverStation.h"
 #include "hal/Encoder.h"
 #include "hal/Errors.h"
+#include "hal/FRCUsageReporting.h"
 #include "hal/HALBase.h"
 #include "hal/I2C.h"
 #include "hal/Interrupts.h"
@@ -41,7 +42,3 @@
 #include "hal/Threads.h"
 #include "hal/Types.h"
 #include "hal/Value.h"
-
-#ifdef __cplusplus
-#include "hal/FRCUsageReporting.h"
-#endif