Switch to Debian Stretch sysroot

This CL switches the default sysroot from Jessie to Stretch.
There are no deps changes.  The libstdc++ requirement is not
affected because we do an in-tree build of libc++ instead.
The glibc requirement is also not changed because we don't
currently use any of the symbols from the newer version.

BUG=751812
R=dpranke@chromium.org,thestig@chromium.org
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_chromium_archive_rel_ng;master.tryserver.chromium.linux:linux_arm

Change-Id: I89da578852fe0f7bfd27ffc08fda99e3b4df239e
Reviewed-on: https://chromium-review.googlesource.com/598737
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516093}
2 files changed