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.

system/hexed/src/hexed.c

@@ -371,11 +371,7 @@ int runargs(void)
 
 /* hexed - Hexadecimal File Editor */
 
-#ifdef BUILD_MODULE
 int main(int argc, FAR char *argv[])
-#else
-int hexed_main(int argc, char *argv[])
-#endif
 {
   struct cmdargs_s args;