Small MSVC build fixes.

- "/Ox /O2 /Ob2" get's reduced to "/O2", the reason being:

    /Ox = /Ob2 /Og /Oi /Ot /Oy /Gs
    /O2 = /Ob2 /Og /Oi /Ot /Oy /Gs /GF /Gy

- apps/openssl.cnf gets installed.

- always delete files quietly, as they might not be there.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1075)