Compiler warnings currently go unnoticed in our macOS builds, since -Werror
is only enabled for Linux and MinGW builds by default. So let's enable them
here now, too.
Unfortunately, the sasl header is marked as deprecated in the macOS headers
and thus generates a lot of deprecation warnings. Thus we have to also use
-Wno-error=deprecated-declarations to be able to compile the code here.

Message-Id: <20200728074405.13118-4-thuth@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>