openssl: set FLAG_TRUSTED_FIRST unconditionally

openssl: set FLAG_TRUSTED_FIRST unconditionally

On some systems, openssl 1.0.x is still the default, but it has been
patched to contain all the recent security fixes. As a result of this
patching, it is possible for macro X509_V_FLAG_NO_ALT_CHAINS to be
defined, while the previous behavior of openssl to not look at trusted
chains first, remains.

Fix it: ensure X509_V_FLAG_TRUSTED_FIRST is always set, do not try to
probe for the behavior of openssl based on the existence ofmacros.

Closes #5530