Support Trusty, an embedded platform.

Trusty doesn't have setjmp.h and nor does it have threads.

Change-Id: I005f7a009a13e6632513be9fab2bbe62294519a4
Reviewed-on: https://boringssl-review.googlesource.com/4660
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/include/openssl/asn1.h b/include/openssl/asn1.h
index 7c62161..4baf81c 100644
--- a/include/openssl/asn1.h
+++ b/include/openssl/asn1.h
@@ -61,6 +61,8 @@
 
 #include <openssl/base.h>
 
+#include <time.h>
+
 #include <openssl/bio.h>
 #include <openssl/stack.h>