OpenSSL and CURL are not downloaded

[schnelle]

The current CMake build file is already prepared to ad hoc compile OpenSLL and CURL but compilation failed on a Windows11 machine as the file names exceeded 256 characters which is a known limitiation on Windows.

Until then, the CURL must be downloaded and include and library files must be made known to CMake via

• CURL_INCLUDE_DIR
• CURL_LIBRARY