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This fixes the following issue:
- allow forwarder2 to compile with clang
- Makes android executables position independant so that they can be run
  on android devices
- Add missing BUILD.gn

TBR=brettw@chromium.org

Review URL: https://codereview.chromium.org/684133002

Cr-Commit-Position: refs/heads/master@{#302429}