external/openssh: update to 6.8p1.

In preparation for some updates to external/openssh to make it work with
BoringSSL, this change updates the code to a recent version. The current
version (5.9p1) is coming up on four years old now.

  * Confirmed that f5c67b478bef9992de9e9ec91ce10af4f6205e0d matches
    OpenSSH 5.9p1 exactly (save for the removal of the scard
    subdirectory).

  * Downloaded openssh-6.8p1.tar.gz (SHA256:
    3ff64ce73ee124480b5bf767b9830d7d3c03bbcb6abe716b78f0192c37ce160e)
    and verified with PGP signature. (I've verified Damien's key in
    person previously.)

  * Applied changes between f5c67b478bef9992de9e9ec91ce10af4f6205e0d and
    OpenSSH 5.9p1 to 6.8p1 and updated the build as best I can. The
    ugliest change is probably the duplication of umac.c to umac128.c
    because Android conditionally compiles that file twice. See the
    comment in those files.

Change-Id: I63cb07a8118afb5a377f116087a0882914cea486
diff --git a/chacha.h b/chacha.h
new file mode 100644
index 0000000..40eaf2d
--- /dev/null
+++ b/chacha.h
@@ -0,0 +1,35 @@
+/* $OpenBSD: chacha.h,v 1.3 2014/05/02 03:27:54 djm Exp $ */
+
+/*
+chacha-merged.c version 20080118
+D. J. Bernstein
+Public domain.
+*/
+
+#ifndef CHACHA_H
+#define CHACHA_H
+
+#include <sys/types.h>
+
+struct chacha_ctx {
+	u_int input[16];
+};
+
+#define CHACHA_MINKEYLEN 	16
+#define CHACHA_NONCELEN		8
+#define CHACHA_CTRLEN		8
+#define CHACHA_STATELEN		(CHACHA_NONCELEN+CHACHA_CTRLEN)
+#define CHACHA_BLOCKLEN		64
+
+void chacha_keysetup(struct chacha_ctx *x, const u_char *k, u_int kbits)
+    __attribute__((__bounded__(__minbytes__, 2, CHACHA_MINKEYLEN)));
+void chacha_ivsetup(struct chacha_ctx *x, const u_char *iv, const u_char *ctr)
+    __attribute__((__bounded__(__minbytes__, 2, CHACHA_NONCELEN)))
+    __attribute__((__bounded__(__minbytes__, 3, CHACHA_CTRLEN)));
+void chacha_encrypt_bytes(struct chacha_ctx *x, const u_char *m,
+    u_char *c, u_int bytes)
+    __attribute__((__bounded__(__buffer__, 2, 4)))
+    __attribute__((__bounded__(__buffer__, 3, 4)));
+
+#endif	/* CHACHA_H */
+