Add smoke test for availability of some Unix functions

The goal isn't to do any functional testing, but to have a simple diagnostic
if some Unix platform function isn't available, and to have a record of
success in the outcome file.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

tests/suites/test_suite_platform_unix.data

@@ -0,0 +1,12 @@
+<unistd.h> smoke test
+unistd_available:
+
+# At the time of writing, we don't actually use CLOCK_REALTIME.
+# But it's the only clock that's guaranteed by POSIX.
+clock_gettime(CLOCK_REALTIME) smoke test
+clock_gettime_available:CLOCK_REALTIME
+
+# Used for mbedtls_ms_time() on platforms where we don't think
+# CLOCK_BOOTTIME is available.
+clock_gettime(CLOCK_MONOTONIC) smoke test
+clock_gettime_available:CLOCK_MONOTONIC

tests/suites/test_suite_platform_unix.function

@@ -0,0 +1,45 @@
+/* BEGIN_HEADER */
+/* Test access to the Unix primitives used in platform_util.c and elsewhere.
+ * We aren't testing that they work, just getting an easy-to-understand
+ * diagnostic if they aren't available.
+ * (There is a separate test suite for the platform_util.h interfacces.)
+ */
+
+#include <mbedtls/platform_util.h>
+#include <mbedtls/platform.h>
+#include "common.h"
+
+#if defined(MBEDTLS_PLATFORM_IS_UNIXLIKE)
+
+#include <time.h>
+#include <unistd.h>
+
+#endif /* defined(MBEDTLS_PLATFORM_IS_UNIXLIKE) */
+
+/* END_HEADER */
+
+/* Note: we can't make the whole test suite depend on
+ * MBEDTLS_PLATFORM_IS_UNIXLIKE, because file-level dependencies can only
+ * come from build_info.h, platform.h or some test helper headers, not
+ * from internal macros. */
+/* BEGIN_DEPENDENCIES
+ * END_DEPENDENCIES */
+
+/* BEGIN_CASE depends_on:MBEDTLS_PLATFORM_IS_UNIXLIKE */
+void unistd_available()
+{
+    pid_t pid = getpid();
+    TEST_LE_S(1, pid);
+}
+/* END_CASE */
+
+/* BEGIN_CASE depends_on:MBEDTLS_PLATFORM_IS_UNIXLIKE */
+void clock_gettime_available(int clockid)
+{
+    struct timespec ts = { 0, 0 };
+    memset(&ts, 0, sizeof(ts));
+    int ret = clock_gettime(clockid, &ts);
+    TEST_ASSERT_ERRNO(ret == 0);
+    TEST_LE_S(1, ts.tv_sec);
+}
+/* END_CASE */