gyp

Specifically, this change makes it so that rules explicitly list
 their outputs in the generated Xcode project.

Previously, rules added to Xcode did not list their outputs and this
worked fine because make handled everything correctly. However due to
recent build system improvements made by Apple
(https://developer.apple.com/documentation/xcode_release_notes/xcode_10_release_notes/build_system_release_notes_for_xcode_10?language=objc)
only files explicitly listed as outputs can be referenced in build
targets.

"If an output file which is generated by a shell script is used as an
input elsewhere in the build (for example, to another shell script),
then that output must be declared as an explicit output by the script
that generates it; otherwise the build system may attempt to search for
the file before it has been generated, causing the build to fail."

Change-Id: Ia5c9e8ef604e4268755f11a33ccd2ea9564fd0fe
Reviewed-on: https://chromium-review.googlesource.com/c/1318929


Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>