tools/nolibc: add difftime()

This is used in various selftests and will be handy when integrating
those with nolibc.

Signed-off-by: Thomas Weißschuh <[e-mail]>
Acked-by: Willy Tarreau <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Thomas Weißschuh <[e-mail]>

tools/include/nolibc/time.h

···
 }
 
 
+static __inline__
+double difftime(time_t time1, time_t time2)
+{
+	return time1 - time2;
+}
+
+
 static __attribute__((unused))
 time_t time(time_t *tptr)
 {

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

···
 	return ret;
 }
 
+int test_difftime(void)
+{
+	if (difftime(200., 100.) != 100.)
+		return 1;
+
+	if (difftime(100., 200.) != -100.)
+		return 1;
+
+	return 0;
+}
+
 int run_stdlib(int min, int max)
 {
 	int test;
···
 		CASE_TEST(toupper_noop);            EXPECT_EQ(1, toupper('A'), 'A'); break;
 		CASE_TEST(abs);                     EXPECT_EQ(1, abs(-10), 10); break;
 		CASE_TEST(abs_noop);                EXPECT_EQ(1, abs(10), 10); break;
+		CASE_TEST(difftime);                EXPECT_ZR(1, test_difftime()); break;
 
 		case __LINE__:
 			return ret; /* must be last */