selftests/nolibc: stat_timestamps: remove procfs dependency

'/proc/self/' is a good path which doesn't have stale time info but it
is only available for CONFIG_PROC_FS=y.

When CONFIG_PROC_FS=n, use argv0 instead of '/proc/self', use '/' for the
worst case.
Reviewed-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Zhangjin Wu <falcon@tinylab.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>

tools/testing/selftests/nolibc/nolibc-test.c

@@ -584,7 +584,7 @@ static int test_stat_timestamps(void)
 	if (sizeof(st.st_atim.tv_sec) != sizeof(st.st_atime))
 		return 1;
 
-	if (stat("/proc/self/", &st))
+	if (stat("/proc/self/", &st) && stat(argv0, &st) && stat("/", &st))
 		return 1;
 
 	if (st.st_atim.tv_sec != st.st_atime || st.st_atim.tv_nsec > 1000000000)