cmake: fix HAVE_GETHOSTNAME definition

Otherwise Curl_gethostname always fails. Windows has gethostname
since Vista according to
http://msdn.microsoft.com/en-us/library/ms738527%28VS.85%29.aspx, but
accordings to byte_bucket's VC 2005 documentation, it is available even
in Windows 95. (possibly after installing a Platform SDK, the
Windows Server 2003 SP1 Platform SDK should be sufficient).

Signed-off-by: Peter Wu <peter@lekensteyn.nl>

CMake/Platforms/WindowsCache.cmake

@@ -5,6 +5,7 @@ if(NOT UNIX)
     set(HAVE_LIBSOCKET 0)
     set(NOT_NEED_LIBNSL 0)
     set(HAVE_LIBNSL 0)
+    set(HAVE_GETHOSTNAME 1)
     set(HAVE_LIBZ 0)
     set(HAVE_LIBCRYPTO 0)