changed default behaviour for clock_gettime()

CMake now checks first for clock_gettime() in librt, so
we can make use of its capabilities when available.

CMakeLists.txt

@@ -36,18 +36,18 @@ else(SSL MATCHES "openssl")
   endif(POLARSSL_FOUND)
 endif(SSL MATCHES "openssl")
 
-check_function_exists(clock_gettime HAVE_CLOCK_GETTIME)
+check_library_exists(rt clock_gettime "time.h" HAVE_CLOCK_GETTIME_RT)
 
-if(NOT HAVE_CLOCK_GETTIME)
-  check_library_exists(rt clock_gettime "time.h" HAVE_CLOCK_GETTIME_RT)
-  if(NOT HAVE_CLOCK_GETTIME_RT)
+if(NOT HAVE_CLOCK_GETTIME_RT)
+  check_function_exists(clock_gettime HAVE_CLOCK_GETTIME)
+  if(NOT HAVE_CLOCK_GETTIME)
     check_library_exists(c clock_get_time "mach/time.h" HAVE_CLOCK_GET_TIME)
     if(NOT HAVE_CLOCK_GET_TIME)
       message(FATAL_ERROR "Didn't find clock_gettime() or clock_get_time!")
     endif()
-  else()
-    set(LIBRT rt)
   endif()
+else()
+  set(LIBRT rt)
 endif()
 
 set(SOURCE "")