Initially, a full bulk build was run with security/libressl 2.6.4 so it could be compared with the failures of the security/libressl-devel 2.7.0 bulk build.<<BR> LibreSSL 2.6.4 reference poudriere logs
LibreSSL 2.7.0 first full build logs

Looks like failure is triggered on clang 6 and later. Reported by Daniel Stenberg of cURL and Kris Moore of TrueOS for Apache 2.4.33.

Observed on MacOS by Daniel Stenberg on Apple MacOS

vtls/openssl.c:2805:35: error: passing 'const X509_ALGOR *' (aka 'const struct X509_algor_st *') to parameter of type 'X509_ALGOR *' (aka 'struct X509_algor_st *') discards qualifiers [-Werror,-Wincompatible-pointer-types-discards-qualifiers]
        X509_signature_print(mem, palg, a);
                                  ^~~~
/usr/local/Cellar/libressl/2.7.2/include/openssl/x509.h:670:46: note: passing argument to parameter 'alg' here
int X509_signature_print(BIO *bp,X509_ALGOR *alg, ASN1_STRING *sig);
                                             ^
1 error generated.

Fixed with openssl: provide defines for argument typecasts to build warning-free

Observed by Kris Moore of TrueOS on FreeBSD 12-STABLE (i.e. TrueOS) which has clang 6.

--- ssl_engine_vars.slo ---
ssl_engine_vars.c:536:25: error: passing 'const ASN1_OBJECT **' (aka 'const struct asn1_object_st **') to parameter of type 'ASN1_OBJECT **' (aka 'struct asn1_object_st **') discards qualifiers in nested pointer types [-Werror,-Wincompatible-pointer-types-discards-qualifiers]
        X509_ALGOR_get0(&paobj, NULL, NULL, X509_get0_tbs_sigalg(xs));
                        ^~~~~~
/usr/include/openssl/x509.h:774:36: note: passing argument to parameter 'paobj' here
void X509_ALGOR_get0(ASN1_OBJECT **paobj, int *pptype, void **ppval,
                                   ^
ssl_engine_vars.c:536:45: error: passing 'const X509_ALGOR *' (aka 'const struct X509_algor_st *') to parameter of type 'X509_ALGOR *' (aka 'struct X509_algor_st *') discards qualifiers [-Werror,-Wincompatible-pointer-types-discards-qualifiers]
        X509_ALGOR_get0(&paobj, NULL, NULL, X509_get0_tbs_sigalg(xs));
                                            ^~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/openssl/x509.h:775:19: note: passing argument to parameter 'algor' here
                                                X509_ALGOR *algor);
                                                            ^
2 errors generated.

Work-around: Set CFLAGS+= -Wno-incompatible-pointer-types-discards-qualifiers in port Makefile.