Fixes for gcc 4.8

The use of a non-static function without a declaration generates a
warning for gcc 4.8.

Clang-3.4 does not work when compiling for gprof. The executable always
generates a segv.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/platforms/posix/px4_layer/px4_posix_tasks.cpp

@@ -273,6 +273,7 @@ void px4_show_tasks()
 }
 
 __BEGIN_DECLS
+const char *getprogname();
 const char *getprogname()
 {
         pthread_t pid = pthread_self();