cmake: add CURL_BUILD_EVERYTHING option

[vszakats]

To build all targets in a single go, meaning curl and libcurl as normal,
and tests and examples in addition. To build-test everything without
running multiple cmake commands.

Enable with:

• -DCURL_BUILD_EVERYTHING=ON
  Special values: QUICK to build examples quickly for build test,
  NOEXAMPLES to not build examples.

A well-equipped build takes 2.8s of configure time, and 1.7s to build
everything (shared, unity, ninja, prefill), 1.4s with QUICK. Without
this option it takes <1s to build curl/libcurl.

Also: streamline CURL_LINT internal logic.

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• use the fast examples target or the normal one? maybe both with an option? (reduces build time: 1.7 → 1.4s)

[vszakats]

A fairly-well packed build takes 2.8s of configure time, and 1.7s
to build everything (shared, unity, ninja, prefill). Compared to <1s for
building just curl/libcurl.

It reduces to 1.4s by building the build-test-specific examples target.

For local tests, building everything is a practical option!