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/random/random_main.c

@@ -77,11 +77,7 @@
  * rand_main
  ****************************************************************************/
 
-#ifdef BUILD_MODULE
 int main(int argc, FAR char *argv[])
-#else
-int rand_main(int argc, char *argv[])
-#endif
 {
   uint32_t buffer[CONFIG_EXAMPLES_MAXSAMPLES];
   int nsamples = CONFIG_EXAMPLES_NSAMPLES;