cmake: Fix the build on Windows.
cmake: Fix the build on Windows.

(cherry picked from commit a738507ad24aa283c6af91fc2a5e8b35473d4c77)

mwgoldsmith/ssh,mwgoldsmith/ssh,mwgoldsmith/libssh,mwgoldsmith/libssh,mwgoldsmith/libssh,mwgoldsmith/ssh,mwgoldsmith/ssh,mwgoldsmith/libssh