MSVC: Disable deprecated declarations (C4996) warning

`/wd4996' disables deprecated declarations warning, this is analogous to
`-Wno-error=deprecated-declarations'. Error example:

  gost_pmeth.c(39,17): warning C4996: 'EVP_PKEY_get0': Since OpenSSL 3.0

Signed-off-by: Vitaly Chikunov <vt@altlinux.org>