dril implementation in Mesa 24.2 breaks freeglut's fgOpenWindow()

Summary

This is a follow-up from #11830, running freeglut with Xvfb fails because freeglut cannot find a matching FBconfig anymore.

The same was working in Mesa < 24.2

Steps to reproduce

1. Clone freeglut

$ git clone git clone https://github.com/freeglut/freeglut

2. Build freeglut (and its demo programs)

$ cd freeglut
~/freeglut $ cmake .
~/freeglut $ make

3. Run a demo program in Xvfb

$ cd bin/
~/freeglut/bin $ xvfb-run ./3dview
freeglut (./3dview):  ERROR:  Internal error <FBConfig with necessary capabilities not found> in function fgOpenWindow

(Note if you do not have the helper shell script xvfb-run with your distribution, you can as well run Xvfb and run the demo program on the Xvfb xserver manually)

Actual result

freeglut (./3dview):  ERROR:  Internal error <FBConfig with necessary capabilities not found> in function fgOpenWindow

Expected result

No error

Additional data

I think this is because freeglut's fgOpenWindow() cannot find a matching FBconfig exposed by the new the gallium/dril implementation in Mesa 24.2, see !28378 (merged)

The same works fine with Mesa 24.1

The freeglut's X11 implementation of fgPlatformOpenWindow() (from where the error comes) can be found here:

https://github.com/freeglut/freeglut/blob/master/src/x11/fg_window_x11.c#L139