winbuild: Support custom devel paths for each dependency

- Support custom devel paths for c-ares, mbedTLS, nghttp2, libSSH2,
  OpenSSL and zlib. Respectively: CARES_PATH, MBEDTLS_PATH,
  NGHTTP2_PATH, SSH2_PATH, SSL_PATH and ZLIB_PATH.

- Use lib.exe for making the static library instead of link.exe /lib.
  The latter is undocumented and could cause problems as noted in the
  comments.

- Remove a dangling URL that no longer worked. (I was not able to find
  the IDN download at MSDN/microsoft.com, so it seems to be removed.)

- Remove custom override for release-ssh2-ssl-dll-zlib configuration.
  Nobody knows why it was there and as far as we can see is unnecessary.

Closes https://github.com/curl/curl/pull/2474