Configure: merge all of %user and %useradd into %config earlier

This came about with the realisation that upper case CFLAGS, LDFLAGS
and so on aren't treated much after that, and this makes figuring out
user added flags significantly easier, just look in %config.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/8812)

(cherry picked from commit c1a09254)