Set CMAKE_REQUIRED_DEFINITIONS to include definitions needed to get
the winsock2 API from windows.h. Simplify the order of checks to
avoid extra conditions.
Use check_include_file instead of check_include_file_concat to look
for OpenSSL headers. They do not need to participate in a sequence
of dependent system headers. Also they may cause winsock.h to be
included before ws2tcpip.h, causing the latter to not be detected
in the sequence.
Reviewed-by: Brad King <brad.king@kitware.com>
It tries hard to recognise SDK's on different platforms. On windows MIT
Kerberos installs SDK with other things and puts path into registry.
Heimdal have separate zip archive. On linux pkg-config is tried, then
krb5-config script and finally old-style libs and headers detection.
Command line args:
* CMAKE_USE_GSSAPI - enables GSSAPI detection
* GSS_ROOT_DIR - if set, should point to the root of GSSAPI installation
(the one with include and lib directories)
