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.

patches/x509.h.patch

@@ -1,15 +1,17 @@
 --- include/openssl/x509.h.orig	2015-07-06 13:15:15.059306046 -0700
 +++ include/openssl/x509.h	2015-07-06 13:16:10.506118278 -0700
-@@ -112,6 +112,17 @@
+@@ -112,6 +112,19 @@
  extern "C" {
  #endif
 
-+#if defined(_WIN32) && defined(__WINCRYPT_H__)
++#if defined(_WIN32)
++#ifndef LIBRESSL_INTERNAL
 +#ifdef _MSC_VER
 +#pragma message("Warning, overriding WinCrypt defines")
 +#else
 +#warning overriding WinCrypt defines
 +#endif
++#endif
 +#undef X509_NAME
 +#undef X509_CERT_PAIR
 +#undef X509_EXTENSIONS