Re-ordering the #include's is a bit problematic here because
libpq/libpq-be.h needs to include <openssl/ssl.h>. Instead,
let's #undef the unwanted macro after all the #includes.
This is definitely uglier than the other way, but it should
work despite possible future header rearrangements.
(A look at the openssl headers indicates that X509_NAME is the
only conflicting symbol that we use.)
In passing, remove a related but long-incorrect comment in
pg_backup_archiver.h.
Discussion: https://postgr.es/m/1051867.1635720347@sss.pgh.pa.us
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