Allow .o files for GN generated inputs.

GN checks inputs and sources for files that are in the build directory, and
requires those files be generated by a dependency of the target.

Previously, only the final outputs of a target were considered. But NaCl wants
to compile some CRT code and take one of the intermediate object files as
inputs to a subsequent action. The current code was not aware of the generated
object files.

This patch will check for generated object files when the normal checks for
generated inputs fails.

BUG=579629

Review URL: https://codereview.chromium.org/1607423002

Cr-Commit-Position: refs/heads/master@{#370539}
5 files changed