GUACAMOLE-1841: Create a Cygwin build option.

[jmuehlner]

I was able to build and run this successfully using Cygwin. All other protocols are working correctly, as all required libraries are either provided by Cygwin, or easily built from source.

The main difference here is that Windows named pipes are used for IPC instead of local socket pairs, since these do not work as required in Cygwin/Windows. Many other related changes flow from there.

I would greatly appreciate it if people would review this carefully and give it a try themselves, especially any Windows experts (I am decidedly not one).

TODO:

1. Figure out how to build libwebsockets to enable Kubernetes support.
2. Add a README with build instructions for Cygwin.
3. Figure out how to configure fonts on windows for text-based protocols

[jmuehlner]

Winsock support will be detected on Cygwin, but will induce compilation errors if an attempt is made to actually build with it:

In file included from /usr/include/w32api/winsock2.h:56,
                 from socket-fd.c:35:
/usr/include/w32api/psdk_inc/_fd_types.h:100:2: error: #warning "fd_set and associated macros have been defined in sys/types.      This can cause runtime problems with W32 sockets" [-Werror=cpp]
  100 | #warning "fd_set and associated macros have been defined in sys/types.  \
      |  ^~~~~~~
In file included from socket-fd.c:35:
/usr/include/w32api/winsock2.h:1031:34: error: conflicting types for 'select'; have 'int(int,  fd_set *, fd_set *, fd_set *, const TIMEVAL *)'
 1031 |   WINSOCK_API_LINKAGE int WSAAPI select(int nfds,fd_set *readfds,fd_set *writefds,fd_set *exceptfds,const TIMEVAL *timeout);
      |                                  ^~~~~~
In file included from /usr/include/sys/time.h:49,
                 from socket-fd.c:31:
/usr/include/sys/select.h:80:5: note: previous declaration of 'select' with type 'int(int,  fd_set *, fd_set *, fd_set *, struct timeval *)'
   80 | int select __P ((int __n, fd_set *__readfds, fd_set *__writefds,
      |     ^~~~~~
In file included from socket-fd.c:35:
/usr/include/w32api/winsock2.h:1040:34: error: conflicting types for 'gethostname'; have 'int(char *, int)'
 1040 |   WINSOCK_API_LINKAGE int WSAAPI gethostname(char *name,int namelen);
      |                                  ^~~~~~~~~~~
In file included from /usr/include/unistd.h:4,
                 from guacamole/socket-fntypes.h:31,
                 from guacamole/socket.h:31,
                 from socket-fd.c:23:
/usr/include/sys/unistd.h:286:9: note: previous declaration of 'gethostname' with type 'int(char *, size_t)' {aka 'int(char *, long unsigned int)'}
  286 |  int    gethostname (char *__name, size_t __len);
      |         ^~~~~~~~~~~

[aleitner]

Should probably add a check for if CreateEvent fails.

If it fails, it returns NULL and an error message can be retrieved by calling GetLastError.

[aleitner]

Should probably add a check for if CreateEvent fails.

If it fails, it returns NULL and an error message can be retrieved by calling GetLastError.