libsrdb1: futex warning fix

- added _BSD_SOURCE define if _XOPEN_SOURCE is manually defined
  (the _XOPEN_SOURCE define in db_ut.h caused _BSD_SOURCE to be no
  longer defined in features.h => _USE_MISC not defined =>
  syscall() not declared in unistd.h.)

lib/srdb1/db_ut.h

@@ -45,6 +45,9 @@
  */
 #ifndef __OS_solaris
 	#define _XOPEN_SOURCE 600          /* glibc2 on linux, bsd */
+	#define _BSD_SOURCE 1              /* needed on linux to "fix" the effect
+										 of the above define on 
+										 features.h/unistd.h syscall() */
 #else
 	#define _XOPEN_SOURCE_EXTENDED 1   /* solaris */
 #endif