Support -DCONC_WITH_SSL parameter passed to CMake

Usually it is not needed, but sometimes we need to testing interoperability,
e.g OpenSSL server / SCHANNEL client, or WolfSSL server / OpenSSL client.

cmake/mariadb_connector_c.cmake

@@ -8,15 +8,17 @@ SET(CONC_WITH_SIGNCODE ${SIGNCODE})
 SET(SIGN_OPTIONS ${SIGNTOOL_PARAMETERS})
 SET(CONC_WITH_EXTERNAL_ZLIB ON)
 
-IF(SSL_DEFINES MATCHES "WOLFSSL")
+IF(NOT CONC_WITH_SSL)
+  IF(SSL_DEFINES MATCHES "WOLFSSL")
     IF(WIN32)
       SET(CONC_WITH_SSL "SCHANNEL")
     ELSE()
       SET(CONC_WITH_SSL "GNUTLS") # that's what debian wants, right?
     ENDIF()
-ELSE()
+  ELSE()
     SET(CONC_WITH_SSL "OPENSSL")
     SET(OPENSSL_FOUND TRUE)
+  ENDIF()
 ENDIF()
 
 SET(CONC_WITH_CURL OFF)