add initial CMake and Visual Studio build support

This moves the compatibility include files from include to
include/compat so we can use the awful MS C compiler
<../include/> trick to emulate the GNU #include_next extension.

This also removes a few old compat files we do not need anymore.

include/compat/arpa/inet.h

@@ -0,0 +1,19 @@
+/*
+ * Public domain
+ * arpa/inet.h compatibility shim
+ */
+
+#ifndef _WIN32
+#include_next <arpa/inet.h>
+#else
+#include <win32netcompat.h>
+
+#ifndef AI_ADDRCONFIG
+#define AI_ADDRCONFIG               0x00000400
+#endif
+
+#endif
+
+#ifndef HAVE_INET_PTON
+int inet_pton(int af, const char * src, void * dst);
+#endif

include/compat/arpa/nameser.h

@@ -0,0 +1,23 @@
+/*
+ * Public domain
+ * arpa/inet.h compatibility shim
+ */
+
+#ifndef _WIN32
+#include_next <arpa/nameser.h>
+#else
+#include <win32netcompat.h>
+
+#ifndef INADDRSZ
+#define INADDRSZ 4
+#endif
+
+#ifndef IN6ADDRSZ
+#define IN6ADDRSZ 16
+#endif
+
+#ifndef INT16SZ
+#define INT16SZ	2
+#endif
+
+#endif