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/poll.h

@@ -0,0 +1,63 @@
+/*
+ * Public domain
+ *
+ * poll(2) emulation for Windows
+ *
+ * This emulates just-enough poll functionality on Windows to work in the
+ * context of the openssl(1) program. This is not a replacement for
+ * POSIX.1-2001 poll(2).
+ *
+ * Dongsheng Song <dongsheng.song@gmail.com>
+ * Brent Cook <bcook@openbsd.org>
+ */
+
+#ifndef LIBCRYPTOCOMPAT_POLL_H
+#define LIBCRYPTOCOMPAT_POLL_H
+
+#ifndef _WIN32
+#include_next <poll.h>
+#else
+
+#include <winsock2.h>
+
+/* Type used for the number of file descriptors. */
+typedef unsigned long int nfds_t;
+
+#if !defined(_WIN32_WINNT) || (_WIN32_WINNT < 0x0600)
+/* Data structure describing a polling request. */
+struct pollfd {
+	int fd; /* file descriptor */
+	short events; /* requested events */
+	short revents; /* returned events */
+};
+
+/* Event types that can be polled */
+#define POLLIN 0x001 /* There is data to read. */
+#define POLLPRI 0x002 /* There is urgent data to read. */
+#define POLLOUT 0x004 /* Writing now will not block. */
+
+# define POLLRDNORM 0x040 /* Normal data may be read. */
+# define POLLRDBAND 0x080 /* Priority data may be read. */
+# define POLLWRNORM 0x100 /* Writing now will not block. */
+# define POLLWRBAND 0x200 /* Priority data may be written. */
+
+/* Event types always implicitly polled. */
+#define POLLERR 0x008 /* Error condition. */
+#define POLLHUP 0x010 /* Hung up. */
+#define POLLNVAL 0x020 /* Invalid polling request. */
+
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+int poll(struct pollfd *pfds, nfds_t nfds, int timeout);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* HAVE_POLL */
+
+#endif /* LIBCRYPTOCOMPAT_POLL_H */