Make tests run faster on typical platforms.

Make tests run faster on typical platforms.

Sadly not doable in make as it is notoriously bad at telling
you the parallelism being used by make -j.

If the HARNESS_JOBS environment variable has not been
set, this makes the perl script attempt to figure out how
many cpu's are available on anything windows/linux/macos/bsd like,
and if it can be successfully detected, we use that value.
if not, we use 1 as before.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
(Merged from https://github.com/openssl/openssl/pull/28426)