freetdm: add __USE_BSD to ftdm_os, needed by unistd.h for usleep() and string.h to define strcasecmp()

add -Werror even when the compiler is unknown. This is just a work-around to gcc not being detected
	 as GNU by our current standalone build (not bootstrapped through FreeSWITCH)

libs/freetdm/src/testsangomaboost.c

@@ -48,12 +48,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <errno.h>
-#if defined(__linux__) && !defined(__USE_BSD)
-#define __USE_BSD
-#endif
-#ifndef WIN32
-#include <unistd.h>
-#endif
+
 #include "freetdm.h"