Allow parallell make in Configure

If someone tries this:

    MAKE='make -j8' ./config

then Configure ends up doing this:

    make -j8 links depend gentests

Doing those three in parallell leads to a race condition that may very well
cause issue such as tests not being run (because they all get linked to a
dummy that does nothing instead of the real test).

To mitigate this, execute the three targets in one make call each.

Reviewed-by: Emilia Käsper <emilia@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2332)