Make dependency on openssl for EVP functions explicit

Linking against openssl was not done explicitly and mod_auth_gssapi use failed if mod_ssl wasn't loaded in advance:
httpd[4049]: httpd: Syntax error on line 56 of /etc/httpd/conf/httpd.conf: Syntax error on line 1 of /etc/httpd/conf.modules.d/10-auth_gssapi.conf: Cannot load modules/mod_auth_gssapi.so into server: /etc/httpd/modules/mod_auth_gssapi.so: undefined symbol: EVP_DecryptFinal_ex