plugins/utils.h: avoiding warnings on empty printf statements

while compiling i keep receiving an warning statement as follow:

warning: zero-length gnu_printf format string

using an unorthodox method to remove them

Signed-off-by: Ricardo Maraschini <ricardo.maraschini@gmail.com>

plugins/utils.h

@@ -189,7 +189,7 @@ char *fperfdata (const char *,
     https://www.monitoring-plugins.org/doc/extra-opts.html\n\
     for usage and examples.\n")
 #else
-#define UT_EXTRA_OPTS ""
+#define UT_EXTRA_OPTS " \b"
 #endif
 
 #define UT_THRESHOLDS_NOTES _("\