Add s390x support for cipd client bootstrap script.

This is best-effort only; s390x is still not a supported platform.

CIPD pin bump contains no client changes; just points to a version
which is built for s390x as well our normal platforms.

R=dnj@chromium.org, vadimsh@chromium.org

Bug: 764087
Change-Id: I777246712eea1b39036f3b14b88cbd41c7cf0507
Reviewed-on: https://chromium-review.googlesource.com/661787
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Vadim Shtayura <vadimsh@chromium.org>

cipd

@@ -32,6 +32,9 @@ case $UNAME in
   x86_64|amd64)
     ARCH=amd64
     ;;
+  s390x)  # best-effort support for IBM s390x: crbug.com/764087
+    ARCH=s390x
+    ;;
   arm*)
     ARCH=$UNAME
     ;;

cipd_client_version

@@ -1 +1 @@
-git_revision:cf5b0de14e94b06274d15e84b19449f580576e80
+git_revision:0aa5e4d06ec4d3b90980fcb0d0b7c34a5e65b9e1