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/xmalloc.h b/xmalloc.h
index fb217a4..261dfd6 100644
--- a/xmalloc.h
+++ b/xmalloc.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: xmalloc.h,v 1.13 2006/08/03 03:34:42 deraadt Exp $ */
+/* $OpenBSD: xmalloc.h,v 1.14 2013/05/17 00:13:14 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -19,7 +19,6 @@
 void	*xmalloc(size_t);
 void	*xcalloc(size_t, size_t);
 void	*xrealloc(void *, size_t, size_t);
-void     xfree(void *);
 char	*xstrdup(const char *);
 int	 xasprintf(char **, const char *, ...)
                 __attribute__((__format__ (printf, 2, 3)))