Application.mk and main.c files: Change builtin's entry point from main to xxx_main by macro expansion. This change make the entry point fully compliant with POSIX/ANSI standard.

examples/null/null_main.c

@@ -63,11 +63,7 @@
  * Name: null_main
  ****************************************************************************/
 
-#ifdef BUILD_MODULE
 int main(int argc, char *argv[])
-#else
-int null_main(int argc, char *argv[])
-#endif
 {
   return 0;
 }