Add flags to error on compile with incompatible pointer type  (#4455)

* try something a bit different.

* newer compiler plz

* permute

* fix some warnings

* fix getters on OpenSSL < 1.1.0

* this is getting involved

* given our compiler flags we can't have SSL_CTX_set_cookie_verify_cb
diff --git a/Jenkinsfile b/Jenkinsfile
index f89728f..8bb15d6 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -210,7 +210,7 @@
                                 cd cryptography
                                 CRYPTOGRAPHY_SUPPRESS_LINK_FLAGS=1 \
                                     LDFLAGS="/usr/local/opt/openssl\\@1.1/lib/libcrypto.a /usr/local/opt/openssl\\@1.1/lib/libssl.a" \
-                                    CFLAGS="-I/usr/local/opt/openssl\\@1.1/include -Werror -Wno-error=deprecated-declarations -Wno-error=incompatible-pointer-types -Wno-error=unused-function -Wno-error=unused-command-line-argument -mmacosx-version-min=10.9" \
+                                    CFLAGS="-I/usr/local/opt/openssl\\@1.1/include -Werror -Wno-error=deprecated-declarations -Wno-error=incompatible-pointer-types-discards-qualifiers -Wno-error=unused-function -Wno-error=unused-command-line-argument -mmacosx-version-min=10.9" \
                                     tox -r --  --color=yes --wycheproof-root=../wycheproof
                                 virtualenv .venv
                                 source .venv/bin/activate