msvc: adjust build options to harden binaries

msvc: adjust build options to harden binaries

 - enable hardware-enforced stack protection on
compatible hardware/software (/CETCOMPAT linker option)

 - hash object files with SHA256 (/ZH:SHA_256 compiler option)

 - enable SDL. The required to add

    _CRT_NONSTDC_NO_DEPRECATE
    _CRT_SECURE_NO_WARNINGS
    _WINSOCK_DEPRECATED_NO_WARNINGS

preprocessor definitions. I don't feel like replacing strdup (which is
correct POSIX function) and inet_ntoa (we always pass IPv4 address to
it, inet_ntop will make code more complex)

Above issues were discovered by bitskim.

Before applying this patch, this one must be applied from master:

https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg21774.h
tml

Signed-off-by: Lev Stipakov <lev@openvpn.net>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Message-Id: <20220218235255.334-1-lstipakov@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg23852.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>