- Add "libssh2" name to FindLibSSH2 library search.
On Windows systems, libSSH2 CMake installation may name the library
"LibSSH2".
Prior to this change cmake only checked for name "ssh2". On Linux that
works fine because it will prepend the "lib", but it doesn't do that on
Windows.
Closes https://github.com/curl/curl/pull/4804