What kind of change does this PR introduce?
bugfix

Did you add tests for your changes?
nope! I didn't see any existing tests for processOptions.

If relevant, did you update the documentation?
I did not, but this should make the current docs on the watch options true for Webpack configs that are arrays.

Summary

webpack/webpack#4594 points out that watch options aren't being honored when the
Webpack config is an Array. In cases when it's an array, there may not
be a firstOptions.watchOptions, but there will be an options.watchOptions.

In the current implementation, when the Webpack compiler watch method is
called with watchOptions and the Webpack config is an array, watchOptions
will be true and not an object.

I should also note that I don't have a ton of context into the intentions behind using the watch (which is a boolean) in the case that the other options are absent, and an object if watch is false on both options and firstOptions, so at the very least my goal with this PR is to give someone who has better context the information I found so that they can make a good decision on what's best to do here.

webpack/webpack#4594 (not open, but still broken)

• I also noticed that although the above issue was specific to docker + Windows 10, this isn't working as expected in any system I've tested (in a Docker container, locally on MacOS) when the Webpack config export is an array.

Does this PR introduce a breaking change?

It does not, this should be a seamless fallback in the case when the Webpack config is an array instead of an object that does the right thing when the CLI has watch-* flags.

Testing/Repro

• Created an example repo and added a reproducible commit
• Added a console.log for watchOptions above the call to compiler.watch in webpack-cli
• Ran webpack-watch-poll-cfg from the example repo to verify the watchOptions from a webpack.config.js works as expected and received the following:

yarn run webpack-watch-poll-cfg
yarn run v1.9.4
$ webpack --watch --config webpack-poll.config.js
watch options in compiler: { poll: 1000 }

• Ran webpack-watch-poll-cli from the example repo to verify the watchOptions from a CLI flag (--watch-poll) was incorrect (with an Array config):

yarn webpack-watch-poll-cli
yarn run v1.9.4
$ webpack --watch --watch-poll=500 --config webpack-basic.config.js
watch options in compiler: true
watch options in compiler: true

• Updated the package.json to point to my fork in GitHub in this commit
• Ran yarn install
• Ran webpack-watch-poll-cli from the example repo to verify the watchOptions from a CLI flag (--watch-poll) works as expected with an Array config and received the following:

yarn webpack-watch-poll-cli
yarn run v1.9.4
$ webpack --watch --watch-poll=500 --config webpack-basic.config.js
watch options in compiler: { poll: 500 }