Correct system guessing for darwin64-arm64 target
Correct system guessing for darwin64-arm64 target

Previously the system guessing logic would incorrectly guess
i686-apple-darwin as the fallback for any unspecified architecture
that is a Darwin target

Reviewed-by: Matt Caswell <1fa2ef4755a9226cb9a0a4840bd89b158ac71391@openssl.org>
Reviewed-by: Richard Levitte <5fb523282dd7956571c80524edc2dccfa0bd8234@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/13517)

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl