We received reports that the too generic internal ecdsa_{sign,verify}()
symbol names clash in some static links. The naming here is annoying
because the EC_KEY_METHOD amalgamated the no longer existing ECDH and
ECDSA methods which themselves had poorly chosen method names, still
reflected in public API.

There are various messes here. The ECDSA verify methods are declared
in ec_local.h, whereas the ECDSA sign methods are in ecdsa_local.h
(which is itself pretty useless and really only about EC_KEY_METHOD).
I therefore merged the ECDSA method declarations into ec_local.h and
deleted ecdsa_local.h since I see no real benefit to the latter.
ecdsa.c needs ec_local.h anyway. Having the method declarations next
to EC_KEY_METHOD seems sensible. I left the order as it was, matching
ecdsa.c. The eckey_compute_pubkey() prototype should probably be moved
down.

With one exception I just added an ec_key_ prefix. This leads to a
a repetition of 'key' in ec_key_ecdh_compute_key() which I chose to
live with because it matches the public ECDH_compute_key() (mostly
used by SSH implementations). The exception is ec_key_generate_key()
where I expanded the gen() leading to another _key repetition but
this then matches EC_KEY_generate_key().

Thanks to Rosen Penev for reporting and sending an initial diff.
See also https://github.com/gsliepen/tinc/issues/478

ok jsing

this change drops the exclude regex and just simply checks if the
object files are actually available and then constucts a response
file which we pass for linking and this seems to be good enough
to have reproducible make build output (which is what we want here)

ok tb@