[ITA] glibmm2.4

glibmm2.4 2.54.1 (2017) -> 2.66.8 (2025)

This is the latest in what appears to be the same series. Their ABI 
versioning and compatibility in NEWS is really hard to follow (we missed 
a few episodes over the years). I'm just following what is done on Gentoo:

2.66.8 -> gtkmm2/3
2.78.1 -> gtkmm4

Both rely on the same version of glib2. They can be installed in 
parallel. We don't have gtk4, and unlike someone says "I need this now", 
I think we can skip 2.78.1 (ABI 2.68) and save it for later.

I used 2.66.8 to build pangomm1.4, atkmm1.6, cairomm1.0, gtkmm2, gtkmm3. 
None expressed any complaints about it.

Features the doxygen bug where it hangs unless we toggle DOT_NUM_THREADS 
= 1.

Testsuite:
All tests passed, except one which tries to open /etc/passwd. It doesn't 
exist here, so we drop that specific test. This is not as comprehensive 
as glib2's testsuite (some 34 tests vs 200+).

scallywag:
There's been small updates to dependencies since I got this working 
(#9803), I asked scallywag to rebuild, and it got stuck at "requested" 
(#9896). I am unable to issue cancel ("job cancellation not implemented 
for backend").

cygport file:
https://cygwin.com/cgit/cygwin-packages/glibmm2.4/tree/glibmm2.4.cygport?h=playground&id=cd239cfa572d8644d3a2caa2e7b531e0317d8bac

build log:
https://github.com/cygwin/scallywag/actions/runs/14821254680


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P.B. Lecavalier