listing the WITH_* variables for each package

[Sergey Matveychuk]

Simon Barner wrote:

>>One thing I always find annoying is the necessity to dig through the 
>>Makefiles to look at all the WITH_* variables that are available when 
>>compiling a port.  I think there are a couple easy options to do 
>>something better here.
[cutted]

There is a proposal for this from Jean-Yves Lefort. See a PR/58011.

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