Include libstdc++ in the libraries bundled with delta generator.
Include libstdc++ in the libraries bundled with delta generator.

We have updated the toolchain in the chroot to use a newer version of
libstdc++ than what is installed on our workstations. This means
this additional library is required to generate deltas outside of the
chroot.

BUG=chromium-os:25277
TEST=Generated zip file, and ran contents outside of chroot on my workstation.

Change-Id: I5a90ee355aabd4849a9186a9a66e3dc9b1c51d52
Reviewed-on: https://gerrit.chromium.org/gerrit/14597
Reviewed-by: Eric M. Blake <a9da18479c871fe903d9590822cfe2629c6a4d11@google.com>
Reviewed-by: Eric Blake <a9da18479c871fe903d9590822cfe2629c6a4d11@chromium.org>
Tested-by: Don Garrett <546ec366615570e68497e3c5df9092106a9808f4@chromium.org>
Commit-Ready: Don Garrett <546ec366615570e68497e3c5df9092106a9808f4@chromium.org>

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