Add 'dupbuild' as deprecated warning

[dendy]

Fixup after 8f47d5a

Since v1.12 ninja breaks compatibility with existing generators, particularly bob build system, which always invokes ninja with -w dupbuild=err

See: https://github.com/ARM-software/bob-build/blob/master/bob.bash

This patch should also be applied to the 'release' branch.

[tsniatowski]

This would be nice to have, I think it's unfortunate that #2356 causes a hard breakage for people that were already opting-in to the warning.

[digit-google]

Thank you, this looks good to me, the macOS build failures are unrelated to this PR, and hopefully will be addressed shortly.

[digit-google]

PR #2479 was submitted to fix the MacOS issue, please rebase on top of current origin/master and re-upload to get the checks to pass.

[dendy]

Rebased, all tests passed.

[mcprat]

commit message doesn't need the last line about backporting

and if you want to be very formal See: can be replaced with Link:

[dendy]

commit message doesn't need the last line about backporting

Agree, was hesitating about that, but decided to add that line for better visibility. Will remove.

and if you want to be very formal See: can be replaced with Link:

Don't want to be over formal, unless there are strict rules. Any reason to prepend "Link:", isn't it obvious that link is a link? :-) I know people who have a habit to always begin commit body with "Description:" which is silly.

[mcprat]

I agree that is silly... I just mentioned Link: because that's de-facto linux standard tagging and makes it greppable