AP_Common: rearrange headers for consistency

Move attribute definitions all into AP_Common, rather than being split between two files

Remove unused SITL_printf macros

Stop AP_Common including board information

Include AP_Common.h in AP_HAL::Sempahore for WARN_IF_UNUSED; this was the cause of a circular import problem fixed by other commits in this patch.

libraries/AP_Common/AP_Common.h

@@ -20,7 +20,6 @@
 
 #pragma once
 
-#include <AP_HAL/AP_HAL_Boards.h>
 #include <stdint.h>
 #include <stdlib.h>
 
@@ -53,6 +52,20 @@
 #  define FALLTHROUGH
 #endif
 
+#ifdef __GNUC__
+ #define WARN_IF_UNUSED __attribute__ ((warn_unused_result))
+#else
+ #define WARN_IF_UNUSED
+#endif
+
+// use this to avoid issues between C++11 with NuttX and C++10 on
+// other platforms.
+#if !(defined(__GXX_EXPERIMENTAL_CXX0X__) || __cplusplus >= 201103L)
+# define constexpr const
+#endif
+
+#define NORETURN __attribute__ ((noreturn))
+
 #define ToRad(x) radians(x)	// *pi/180
 #define ToDeg(x) degrees(x)	// *180/pi
 
@@ -124,13 +137,3 @@ template<typename s, int t> struct assert_storage_size {
   False otherwise.
 */
 bool is_bounded_int32(int32_t value, int32_t lower_bound, int32_t upper_bound);
-
-/*
-  useful debugging macro for SITL
- */
-#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
-#include <stdio.h>
-#define SITL_printf(fmt, args ...) do { ::printf("%s(%u): " fmt, __FILE__, __LINE__, ##args); } while(0)
-#else
-#define SITL_printf(fmt, args ...)
-#endif