The script freebsd-namespace.sh does namespace munging, by adding the Fssh_ prefix to every symbol in libssh, to prevent collisions with other libraries that link with it.
Upstream OpenSSH commit:
324449a68 ("support OpenSSL 3.x cipher IV API change")
Defines EVP_CIPHER_CTX_get_iv as EVP_CIPHER_CTX_get_updated_iv (if HAVE_EVP_CIPHER_CTX_GET_UPDATED_IV is set in config.h).

This produces a compilation warning about the macro being redefined:

In file included from /usr/src/crypto/openssh/monitor.c:64:
/usr/src/crypto/openssh/openbsd-compat/openssl-compat.h:69:11: warning: 'EVP_CIPHER_CTX_get_iv' macro redefined [-Wmacro-redefined]
   69 | #  define EVP_CIPHER_CTX_get_iv EVP_CIPHER_CTX_get_updated_iv
      |           ^
/usr/src/crypto/openssh/ssh_namespace.h:12:9: note: previous definition is here
   12 | #define EVP_CIPHER_CTX_get_iv                   Fssh_EVP_CIPHER_CTX_get_iv
      |         ^

Avoid the warning by un-defining it before defining it, as done in ee8c73cd0620 ("Silence warnings about redefined macros."), appending the same comment from crypto/openssh/umac128.c for easy grepping.