Windows support

[Kartatz]

Trying to cross-compile to Windows fails with the following error:

-- The C compiler identification is Clang 17.0.1
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /root/llvm-mingw-20230919-msvcrt-ubuntu-20.04-x86_64/bin/x86_64-w64-mingw32-gcc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- curl version=[8.1.1-DEV]
-- Could NOT find Perl (missing: PERL_EXECUTABLE) 
-- Looking for getch in ws2_32;
-- Looking for getch in ws2_32; - found
-- Looking for getch in winmm;ws2_32
-- Looking for getch in winmm;ws2_32 - found
-- Performing Test HAVE_MINGW_ORIGINAL
-- Performing Test HAVE_MINGW_ORIGINAL - Failed
CMake Error at /usr/share/cmake-3.26/Modules/FindPackageHandleStandardArgs.cmake:230 (message):
  Could NOT find OpenSSL, try to set the path to OpenSSL root folder in the
  system variable OPENSSL_ROOT_DIR (missing: OPENSSL_CRYPTO_LIBRARY) (found
  version "")
Call Stack (most recent call first):
  /usr/share/cmake-3.26/Modules/FindPackageHandleStandardArgs.cmake:600 (_FPHSA_FAILURE_MESSAGE)
  /usr/share/cmake-3.26/Modules/FindOpenSSL.cmake:670 (find_package_handle_standard_args)
  submodules/curl/CMakeLists.txt:428 (find_package)
-- Configuring incomplete, errors occurred!

It seems that CMake is complaing about a missing variable:

missing: OPENSSL_CRYPTO_LIBRARY

But this variable is already defined at CMakeLists.txt:102.

Currently, this is the only issue blocking Kad from supporting Windows.