swift234

[build-script] Remove ios/tvos flag from buildbot_incremental_base and
instead have a new preset buildbot_incremental_base_all_platforms that
has those flags.

The reason why this makes sense is:

1. There are a bunch of presets that inherit from
buildbot_incremental_base that do not want to build ios/tvos. So they
turn it off. That is wasteful and bug inducing.

2. I am going to be adding such a bot for OS X smoke tests. It only runs
OS X tests and builds OS X to keep the smoke test time down.