build: make build-addons execute parallel

[danbev]

Currently the building of addons and addons-napi are done sequentially
but could be done in parallel which this commit tries to address.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

Affected core subsystem(s)

build

[danbev]

CI: https://ci.nodejs.org/job/node-test-pull-request/7224/

[thefourtheye]

I am not in favour. Mainly because the compilation logs are interleaved and difficult to understand. That said, I am 0 on this.

[bnoordhuis]

I have a somewhat more rigorous approach in #12231 that also addresses the issue that caused #11628.

[danbev]

Closing in favour of #12231