AP_Common: no c++ magic for PX4 build

libraries/AP_Common/c++.cpp

@@ -9,6 +9,8 @@
 
 #include <stdlib.h>
 
+#ifndef PX4FMU_BUILD
+
 void * operator new(size_t size)
 {
     return(calloc(size, 1));
@@ -47,3 +49,5 @@ void __cxa_guard_release (__guard *g){
 void __cxa_guard_abort (__guard *) {
 };
 
+#endif // PX4FMU_BUILD
+