refs #5710 invariant_zero must not be visible when this header is exported to the handlerton

git-svn-id: file:///svn/toku/tokudb@50464 c7de825b-a66e-492c-adef-691d508d4ae1

portability/toku_time.h

@@ -98,7 +98,7 @@ static inline uint64_t toku_current_time_microsec(void) {
 static inline uint64_t toku_current_time_nanosec(void) {
     struct timespec t;
     int r = toku_clock_gettime(CLOCK_REALTIME, &t);
-    invariant_zero(r);
+    assert(r == 0);
     return t.tv_sec * (1UL * 1000 * 1000 * 1000) + t.tv_nsec;
 }