Do not include time.h without MBEDTLS_HAVE_TIME

MBEDTLS_HAVE_TIME is documented as: "System has time.h and time()."

If that is not defined, do not attempt to include time.h.

A particular problem is platform-time.h, which should only be included if
MBEDTLS_HAVE_TIME is defined, which makes everything messier. Maybe it
should be refactored to have the check inside the header.

Signed-off-by: Daniel Axtens <dja@axtens.net>
diff --git a/include/mbedtls/platform.h b/include/mbedtls/platform.h
index 11a9ca1..a598434 100644
--- a/include/mbedtls/platform.h
+++ b/include/mbedtls/platform.h
@@ -62,7 +62,9 @@
 #if !defined(MBEDTLS_PLATFORM_NO_STD_FUNCTIONS)
 #include <stdio.h>
 #include <stdlib.h>
+#if defined(MBEDTLS_HAVE_TIME)
 #include <time.h>
+#endif
 #if !defined(MBEDTLS_PLATFORM_STD_SNPRINTF)
 #if defined(MBEDTLS_PLATFORM_HAS_NON_CONFORMING_SNPRINTF)
 #define MBEDTLS_PLATFORM_STD_SNPRINTF   mbedtls_platform_win32_snprintf /**< The default \c snprintf function to use.  */