OpenSSL::config: determine the MSVC target architecture by asking cl

OpenSSL::config: determine the MSVC target architecture by asking cl

Since cl knows what architecture it builds fore, all depending on what
the user set up, it makes sense to ask it, and use that result primarly,
and only use the POSIX::uname() MACHINE value as a fallback.

Also, this does indeed determine if cl is present or not.

We drop the explicit names in .github/workflows/windows.yml as proof
of concept.

Fixes #19281

Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19285)