AP_InternalError: improve gating of use of AP_InternalError library

- gate calls into library directly on the define
 - INTERNAL_ERROR becomes empty if library not compiled in

libraries/AP_InternalError/AP_InternalError.cpp

@@ -1,6 +1,12 @@
+#include "AP_InternalError_config.h"
+
+#if AP_INTERNALERROR_ENABLED
+
 #include "AP_InternalError.h"
 
-#include <AP_BoardConfig/AP_BoardConfig.h>
+#include <AP_HAL/HAL.h>
+#include <AP_HAL/Util.h>
+
 #include <stdio.h>
 
 extern const AP_HAL::HAL &hal;
@@ -137,3 +143,5 @@ void AP_memory_guard_error(uint32_t size)
         AP_HAL::panic("memory guard size=%u\n", unsigned(size));
     }
 }
+
+#endif  // AP_INTERNALERROR_ENABLED

libraries/AP_InternalError/AP_InternalError.h

@@ -22,6 +22,10 @@
 
 #pragma once
 
+#include "AP_InternalError_config.h"
+
+#if AP_INTERNALERROR_ENABLED
+
 #include <stdint.h>
 
 class AP_InternalError {
@@ -113,3 +117,7 @@ extern "C" {
 
 #define INTERNAL_ERROR(error_number) \
     AP::internalerror().error(error_number, __AP_LINE__);
+
+#else  // AP_INTERNALERROR_ENABLED is false
+#define INTERNAL_ERROR(error_number)
+#endif // AP_INTERNALERROR_ENABLED

libraries/AP_InternalError/AP_InternalError_config.h

@@ -0,0 +1,7 @@
+#pragma once
+
+#include <AP_HAL/AP_HAL_Boards.h>
+
+#ifndef AP_INTERNALERROR_ENABLED
+#define AP_INTERNALERROR_ENABLED 1
+#endif