Allow the res argument to clock_getres() to be NULL.

libc/sysdeps/linux/common/clock_getres.c

@@ -18,15 +18,18 @@ libc_hidden_proto(sysconf)
 
 int clock_getres(clockid_t clock_id, struct timespec* res)
 {
-	long clk_tck;
 	int retval = -1;
 
 	switch (clock_id) {
 		case CLOCK_REALTIME:
-			if ((clk_tck = sysconf(_SC_CLK_TCK)) < 0)
-				clk_tck = 100;
-			res->tv_sec = 0;
-			res->tv_nsec = 1000000000 / clk_tck;
+			if (res) {
+				long clk_tck;
+
+				if ((clk_tck = sysconf(_SC_CLK_TCK)) < 0)
+					clk_tck = 100;
+				res->tv_sec = 0;
+				res->tv_nsec = 1000000000 / clk_tck;
+			}
 			retval = 0;
 			break;