Add X509_V_FLAG_NO_CHECK_TIME.

This was added in OpenSSL 1.1.0. cryptography.io binds it. They don't
actually use it, but this is a useful feature to have anyway. Projects
like Envoy currently implement such a mode with
X509_STORE_set_verify_cb, which is a very problematic API to support.
Add this so we can move them to something more sustainable.

Change-Id: Iaff2d08daa743e0b5f4be261cb785fdcd26a8281
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/53965
Commit-Queue: Adam Langley <agl@google.com>
Auto-Submit: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/include/openssl/x509.h b/include/openssl/x509.h
index 96b7495..57eb002 100644
--- a/include/openssl/x509.h
+++ b/include/openssl/x509.h
@@ -2582,6 +2582,10 @@
 // will force the behaviour to match that of previous versions.
 #define X509_V_FLAG_NO_ALT_CHAINS 0x100000
 
+// X509_V_FLAG_NO_CHECK_TIME disables all time checks in certificate
+// verification.
+#define X509_V_FLAG_NO_CHECK_TIME 0x200000
+
 #define X509_VP_FLAG_DEFAULT 0x1
 #define X509_VP_FLAG_OVERWRITE 0x2
 #define X509_VP_FLAG_RESET_FLAGS 0x4