Windows bulding: Make dependency generation not quite as talkative

Windows bulding: Make dependency generation not quite as talkative

The modified way to generate .d files had an unfortunate side effect,
that it outputs the whole preprocessed file and not just the dependency
lines, at least with MSVC's cl.  That gave util/add-depends.pl a whole
lot more to read through, which impacts greatly on the performance of
dependency treatment.

We modify the process by adding a config target attribute 'make_depend',
which can be any suitable command for generating such lines.  All it
needs is to also accept C flags and macro definitions.

Fixes #14994

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/15006)