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/win32netcompat.h

@@ -0,0 +1,48 @@
+/*
+ * Public domain
+ *
+ * BSD socket emulation code for Winsock2
+ * Brent Cook <bcook@openbsd.org>
+ */
+
+#ifndef LIBCRYPTOCOMPAT_WIN32NETCOMPAT_H
+#define LIBCRYPTOCOMPAT_WIN32NETCOMPAT_H
+
+#ifdef _WIN32
+
+#include <ws2tcpip.h>
+
+#define SHUT_RDWR SD_BOTH
+#define SHUT_RD   SD_RECEIVE
+#define SHUT_WR   SD_SEND
+
+#include <errno.h>
+#include <unistd.h>
+
+int posix_connect(int sockfd, const struct sockaddr *addr, socklen_t addrlen);
+
+int posix_close(int fd);
+ssize_t posix_read(int fd, void *buf, size_t count);
+
+ssize_t posix_write(int fd, const void *buf, size_t count);
+
+int posix_getsockopt(int sockfd, int level, int optname,
+	void *optval, socklen_t *optlen);
+
+int posix_setsockopt(int sockfd, int level, int optname,
+	const void *optval, socklen_t optlen);
+
+#ifndef NO_REDEF_POSIX_FUNCTIONS
+#define connect(sockfd, addr, addrlen) posix_connect(sockfd, addr, addrlen)
+#define close(fd) posix_close(fd)
+#define read(fd, buf, count) posix_read(fd, buf, count)
+#define write(fd, buf, count) posix_write(fd, buf, count)
+#define getsockopt(sockfd, level, optname, optval, optlen) \
+	posix_getsockopt(sockfd, level, optname, optval, optlen)
+#define setsockopt(sockfd, level, optname, optval, optlen) \
+	posix_setsockopt(sockfd, level, optname, optval, optlen)
+#endif
+
+#endif
+
+#endif