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/verify.c b/verify.c
new file mode 100644
index 0000000..1671a41
--- /dev/null
+++ b/verify.c
@@ -0,0 +1,49 @@
+/* $OpenBSD: verify.c,v 1.3 2013/12/09 11:03:45 markus Exp $ */
+
+/*
+ * Public Domain, Author: Daniel J. Bernstein
+ * Copied from nacl-20110221/crypto_verify/32/ref/verify.c
+ */
+
+#include "includes.h"
+
+#include "crypto_api.h"
+
+int crypto_verify_32(const unsigned char *x,const unsigned char *y)
+{
+  unsigned int differentbits = 0;
+#define F(i) differentbits |= x[i] ^ y[i];
+  F(0)
+  F(1)
+  F(2)
+  F(3)
+  F(4)
+  F(5)
+  F(6)
+  F(7)
+  F(8)
+  F(9)
+  F(10)
+  F(11)
+  F(12)
+  F(13)
+  F(14)
+  F(15)
+  F(16)
+  F(17)
+  F(18)
+  F(19)
+  F(20)
+  F(21)
+  F(22)
+  F(23)
+  F(24)
+  F(25)
+  F(26)
+  F(27)
+  F(28)
+  F(29)
+  F(30)
+  F(31)
+  return (1 & ((differentbits - 1) >> 8)) - 1;
+}