Add compat bits for libtls on Windows

tls/compat/pwrite.c

@@ -0,0 +1,23 @@
+/*
+ * Public domain
+ *
+ * Kinichiro Inoguchi <inoguchi@openbsd.org>
+ */
+
+#include <unistd.h>
+
+ssize_t
+pwrite(int d, const void *buf, size_t nbytes, off_t offset)
+{
+	off_t cpos, opos, rpos;
+	ssize_t bytes;
+	if((cpos = lseek(d, 0, SEEK_CUR)) == -1)
+		return -1;
+	if((opos = lseek(d, offset, SEEK_SET)) == -1)
+		return -1;
+	if((bytes = write(d, buf, nbytes)) == -1)
+		return -1;
+	if((rpos = lseek(d, cpos, SEEK_SET)) == -1)
+		return -1;
+	return bytes;
+}