Use ASN1_STRING_get0_data for openssl-1.1.0

This fixes a build failure from undefined references to ASN1_STRING_data in
libopusurl.so.

ASN1_STRING_data is deprecated in openssl-1.1.0. The new ASN1_STRING_get0_data
is identical, except the returned string may not be modified, which we don't
do anyway.

Also include missing asn1.h header to silence compiler warnings.

X-Gentoo-Bug: 592456
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=592456