RFR: 8348586: Optionally silence make warnings about non-control variables

[Magnus Ihse Bursie]

On Fri, 24 Jan 2025 17:08:42 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

> When you set a variable on the make command line that is not a known control variable, make emits a note like this:
> 
> 
> Note: Command line contains non-control variables:
> * MODULES=
> * IDEA_OUTPUT=/mnt/h/openjdk/git-jdk2/.idea
> Make sure it is not mistyped, and that you intend to override this variable.
> 'make help' will list known control variables.
> 
> 
> Since [JDK-8347825](https://bugs.openjdk.org/browse/JDK-8347825), this happens whenever you run idea.sh, and it is confusing to users.
> 
> I introduce a general way of silencing such complaints using the new control variable `ALLOW`, and start by applying it on the idea.sh script.

The difference between INIT_CONTROL_VARIABLES and MAKE_CONTROL_VARIABLES had been messed up over the years, so I cleaned that up as well. Since this has worked nevertheless it is likely that this distinction is not needed (anymore?), but at any rate it is informative about where responsibility lies so I kept it.

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PR Comment: https://git.openjdk.org/jdk/pull/23302#issuecomment-2613013238