Add support for Ninja Multi-Config

[KazNX]

The Ninja Multi-Config generator was introduced as part of CMake 3.17 supporting debug and release artefacts under the same build directory, like Xcode or Visual Studio. This change allows colcon to recognise Ninja Multi-Config as a mult-config generator and as a Ninja generator.

Note that in practice this change does not support an apt-get install of CMake on versions of current Ubuntu LTS releases - Unbutu 20.04 (latest current LTS) provided CMake version 3.16.

Change summary:

• Add Ninja Multi-Config to the set of generators where is_multi_configuration_generator() is True

[KazNX]

Checking failures. Not sure how to enforce these locally. I am running a linter.

[KazNX]

I don't think the flake8 failures are due to code I've introduced in the PR. Please advise.

[KazNX]

PR has been rebased onto master fixing the CI check failures.

[hidmic]

Note that in practice this change does not support an apt-get install of CMake on versions of current Ubuntu LTS releases - Unbutu 20.04 (latest current LTS) provided CMake version 3.16.

Hmm, IIUC the change should be transparent for earlier versions -- the generator simply won't ever match.

[hidmic]

@dirk-thomas thoughts before merging?

[KazNX]

Note that in practice this change does not support an apt-get install of CMake on versions of current Ubuntu LTS releases - Unbutu 20.04 (latest current LTS) provided CMake version 3.16.

Hmm, IIUC the change should be transparent for earlier versions -- the generator simply won't ever match.

This was something I was thinking about. The explicitly check for Ninja Multi-Config is fine because we only want to report this explicit generator as being a multi-condig ninja generator.

The compatibility issue is more to make sure Ninja Multi-Config is recognised as also being Ninja.

When I was looking, I found this line (pre-existing this PR).

Note the check is if 'Ninja' in generator and not a straight equality test, so this will match both.

That said, in reviewing your comment I found this line is an equality test. Will fix.