Make it possible to add env var assignments as Configure options
Make it possible to add env var assignments as Configure options

In other words, make the following possible:

    ./config CC=clang

or

    ./Configure CC=clang linux-x86_64

Reviewed-by: Andy Polyakov <015edf36635e030d5e009e08808a59984e629740@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4818)

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