GitLab

* make gperf.py call generate_gperf() both when it's invoked via
  use_jinja_gperf_template() as well as when it's called directly
  as a standalone script

* make generate_gperf() do massaging of gperf's output to remove
  uses of the `register` keyword (needed to build with -std=c++17)
  and replace `/*FALLTHROUGH*/` with real FALLTHROUGH statements
  (needed for -Wimplicit-fallthrough)

* remove now-unneeded suppressions for -Wdeprecated-register

* remove TODO about removing gperf.py; that's from a time when the
  script was 1 non-comment line long

* bump check_output() requirement in comment to 3.4 (since that added
  the input= parameter)

* add missing dependency on gperf.py to build steps calling it
  through the jinja interface, so that these edges rerun when
  gperf.py gets modified

* add a comment mentioning gperf.py at the start of the generated
  outputs

* make :character_data not call gperf.py since it doesn't use gperf,
  and make it use compiled_action() instead which is made for
  exactly character_data's use case

No intended behavior change.

Bug: 752720,177475
Change-Id: I56372729bb47787e2d41a5dff2f30804574770f0
Reviewed-on: https://chromium-review.googlesource.com/891141
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Darren Shen <shend@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533269}