Build unit tests in mingw Windows build

Build unit tests in mingw Windows build

- Minor changes to the build system to include some
  dependencies for Windows build

- test_tls_crypt not built as it will pull in win32.c and
  its dependencies

- If cross-compiling, "make check" will only build the tests but not
  run any. Copy to Windows and run manually. Executables are in
  <buid-dir>/tests/unit_tests/openvpn/.libs/ and these depend on
  cmocka.dll in addition to openssl libs that some tests link to.

  Building with mingw on Windows should run the tests (untested).

v2: networking_testdriver was mistakenly enabled to run, while
originally it was only set to build. Corrected.

v3: exclude check_engine_keys.sh when cross-compiling
As suggested by Arne Schwabe <arne@rfc2549.org>

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <20230208005925.393200-1-selva.nair@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg26188.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>