Update GN bootstrap build

Bootstrap didn't work due to recent modifications in base.
Unfortunately some new dependencies are required on OSX
and that required adding generated_build_date.h to be
available separately for the bootstrap process.

Tested on Linux and OSX.

BUG=None
TEST=./tools/gn/bootstrap/bootstrap.py
R=brettw@chromium.org,tfarina@chromium.org

Review URL: https://codereview.chromium.org/1692303004

Cr-Original-Commit-Position: refs/heads/master@{#376133}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: cda4afd7efda6e3034d58d9f375b01ff3f36d220
1 file changed
tree: 79f06d2a2544c2dc985ef98ee4065a6b970c03e4
  1. tools/