Log Message:
pkg_install: Fix OpenSSL 1.1.0 build

OpenSSL 1.1.0 makes xkusage and ex_flags opaque.

Use X509_check_ca rather than a custom and nearly identical implementation.
This is available since OpenSSL 0.9.8 (even in RHEL5).

This is also done because we cannot implement it identically under
OpenSSL 1.1.0 due to missing getters.

Test EXFLAG_XKUSAGE rather than zero xkusage test no usage to avoid openssl
1.1.0 getter returning a different code on this case.

Use getter for xkusage in the non-zero test case.

Provide fallback definitions for getters.

PR pkg/52298, PR pkg/52648