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.

libtls-standalone/include/string.h

@@ -3,11 +3,15 @@
  * string.h compatibility shim
  */
 
-#include_next <string.h>
-
 #ifndef LIBCRYPTOCOMPAT_STRING_H
 #define LIBCRYPTOCOMPAT_STRING_H
 
+#ifdef _MSC_VER
+#include <../include/string.h>
+#else
+#include_next <string.h>
+#endif
+
 #include <sys/types.h>
 
 #if defined(__sun) || defined(__hpux)
@@ -17,6 +21,11 @@
 #include <strings.h>
 #endif
 
+#ifndef HAVE_STRCASECMP
+int strcasecmp(const char *s1, const char *s2);
+int strncasecmp(const char *s1, const char *s2, size_t len);
+#endif
+
 #ifndef HAVE_STRLCPY
 size_t strlcpy(char *dst, const char *src, size_t siz);
 #endif