Fix running package.py on Windows after https://codereview.chromium.org/1169353002
Fix running package.py on Windows after https://codereview.chromium.org/1169353002

The explicit copied env seems to mess with running cmake, probably
because the setenv.cmd call won't have the same effect in this case.
(cmake just dies without any output though -- it stops dying with
this change here.)

Also change update.py to not buffer stdout at all, so that update.py's
output makes sense combined with the output of its child processes.

BUG=494442
R=hans@chromium.org

Review URL: https://codereview.chromium.org/1187933002.

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#334476}

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