Enable stricter compiler warnings by default

Enable stricter compiler warnings by default

This by default enables the compiler warnings one could previously
enable using the --enable-strict configure option.  I think it is
okay to do so now, because we've taken care of many warnings in the
more standard builds.  (Most of those were totally harmless, but they
prevented us from spotting new more serious mistakes.)

The --enable-strict flag now enables two extra warning flags that I
think can be useful:

-Wsign-compare warns when the compiler promotes a signed type to
unsigned before comparing, which can lead to unexpected behaviour.

-Wuninitialized adds extra warnings about usage of uninitialized variables
or struct elements.

Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: Selva Nair <selva.nair@gmail.com>
Message-Id: <20180201154521.7642-1-steffan@karger.me>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg16426.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>