Add noreturn attribute to fix compiler warnings

configure.ac

@@ -20,6 +20,7 @@ AX_COMPILER_FLAGS
 AC_CANONICAL_HOST
 AX_GCC_FUNC_ATTRIBUTE([constructor])
 AX_GCC_FUNC_ATTRIBUTE([format])
+AX_GCC_FUNC_ATTRIBUTE([noreturn])
 
 AC_MSG_NOTICE([Detected host OS is ${host_os}])
 build_linux=no

daemon/x52d_main.c

@@ -34,6 +34,9 @@ static void set_log_file(bool foreground, const char *log_file)
     }
 }
 
+#if HAVE_FUNC_ATTRIBUTE_NORETURN
+__attribute__((noreturn))
+#endif
 static void usage(int exit_code)
 {
     fprintf(stderr,