test: make clock_lowres.test tap-compatible

NO_DOC=internal
NO_CHANGELOG=internal

test/unit/clock_lowres.c

-#include "unit.h"
-
 #include <math.h>
 #include <unistd.h>
 #include "clock_lowres.h"
 #include "clock.h"
 
+#define UNIT_TAP_COMPATIBLE 1
+#include "unit.h"
+
 /** Test duration in seconds. */
 #define TEST_LEN 1.5
 

test/unit/clock_lowres.result

-1..1
-ok 1 - Check that monotonic lowres clock does not diverge too much from monotonic clock