Add compat bits for libtls on Windows

tls/compat/ftruncate.c

@@ -0,0 +1,13 @@
+/*
+ * Public domain
+ *
+ * Kinichiro Inoguchi <inoguchi@openbsd.org>
+ */
+
+#include <unistd.h>
+
+int
+ftruncate(int fd, off_t length)
+{
+	return _chsize(fd, length);
+}