canon-host problems in cygwin

[Eric Blake]

Cygwin compilation of the canon-host module is giving
warnings that need to be resolved:

$ CFLAGS='-Wall' ./gnulib-tool --test canon-host
...
checking ws2tcpip.h usability... no
checking ws2tcpip.h presence... yes
configure: WARNING: ws2tcpip.h: present but cannot be compiled
configure: WARNING: ws2tcpip.h:     check for missing prerequisite headers?
configure: WARNING: ws2tcpip.h: see the Autoconf documentation
configure: WARNING: ws2tcpip.h:     section "Present But Cannot Be Compiled"
configure: WARNING: ws2tcpip.h: proceeding with the preprocessor's result
configure: WARNING: ws2tcpip.h: in the future, the compiler will take precedence
configure: WARNING:     ## -------------------------------- ##
configure: WARNING:     ## Report this to the dummy lists.  ##
configure: WARNING:     ## -------------------------------- ##
checking for ws2tcpip.h... yes
checking winsock2.h usability... no
checking winsock2.h presence... yes
configure: WARNING: winsock2.h: present but cannot be compiled
configure: WARNING: winsock2.h:     check for missing prerequisite headers?
configure: WARNING: winsock2.h: see the Autoconf documentation
configure: WARNING: winsock2.h:     section "Present But Cannot Be Compiled"
configure: WARNING: winsock2.h: proceeding with the preprocessor's result
configure: WARNING: winsock2.h: in the future, the compiler will take precedence
configure: WARNING:     ## -------------------------------- ##
configure: WARNING:     ## Report this to the dummy lists.  ##
configure: WARNING:     ## -------------------------------- ##
checking for winsock2.h... yes
configure: checking how to do getaddrinfo
checking for library containing getaddrinfo... no
checking for getaddrinfo... no
checking for getaddrinfo in ws2tcpip.h and -lws2_32... yes
...

My understanding of cygwin is that ws2tcpip.h and winsock2.h
should not be used in a typical cygwin program (they should
only be used in mingw or native Windows compilation).

Currently, cygwin does not provide getaddrinfo.  I'm not sure
it is a good idea for cygwin to start linking in ws2_32,
since that library was not compiled with cygwin in mind.
I'm hoping that the upcoming cygwin-1.5.20 will have
getaddrinfo, but in the meantime, it is better to use
the gnulib version of getaddrinfo rather than linking
in incompatible headers and libraries.

--
Eric Blake