FTBFS with openssl 3

sendmail 8.16.1 fails to build with openssl 3 in jammy[1]:

Among the various deprecation warnings, there are several errors in sendmail/tls.c:

tls.c:99:11: error: invalid use of incomplete typedef ‘DH’ {aka ‘struct dh_st’}
   99 | dh->p = BN_bin2bn(dh512_p, sizeof(dh512_p), NULL);
      | ^~
tls.c:100:11: error: invalid use of incomplete typedef ‘DH’ {aka ‘struct dh_st’}
  100 | dh->g = BN_bin2bn(dh512_g, sizeof(dh512_g), NULL);
      | ^~
tls.c:101:16: error: invalid use of incomplete typedef ‘DH’ {aka ‘struct dh_st’}
  101 | if ((dh->p == NULL) || (dh->g == NULL))
      | ^~
tls.c:101:35: error: invalid use of incomplete typedef ‘DH’ {aka ‘struct dh_st’}

Version 8.17.1, currently in debian experimental, builds fine, albeit still with the deprecation warnings.

1. https://launchpadlibrarian.net/596601233/buildlog_ubuntu-jammy-amd64.sendmail_8.16.1-2ubuntu2_BUILDING.txt.gz