Configure: do not check for an absolute prefix in cross-builds

Configure: do not check for an absolute prefix in cross-builds

The check is always made according to the host platform's rules, which may
not be true for true when the target platform is different, e.g. when
cross-building for Windows on a Linux machine. So skip this check when
used together with the `--cross-compile-prefix=` option.

Fixes https://github.com/openssl/openssl/issues/9520

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22723)