apps/openssl.c: UTF-y Windows argv.

Windows never composes UTF-8 strings as result of user interaction
such as passing command-line argument. The only way to compose one
is programmatic conversion from WCHAR string, which in turn can be
picked up on command line.

[For reference, why not wmain, it's not an option on MinGW.]

Reviewed-by: Richard Levitte <levitte@openssl.org>