Fix XFA builds under chromium checkouts

This pulls in from origin/master:
94dd28e Update GN build files w/ cpu_arch -> current_cpu changes.
1e580a1 Fix multiply defined macro in zlib.h

Add a missing file to BUILD.gn dropped at 1ed8a21.

TBR=thestig@chromium.org

Review URL: https://codereview.chromium.org/1189133006.
2 files changed