Fringe bitmap scaling

[Yuri Khan]

Hello list,

I’m using Emacs 29.1 on Ubuntu 22.04, X11, HiDPI monitor.

    $ xdpyinfo | grep -i resolution
      resolution:    192x193 dots per inch
    $ xrdb -get Xft.dpi
    192
    $ env | grep SCALE
    GDK_DPI_SCALE=0.5

If I compile Emacs with the default GTK+ toolkit, the fringe icons are
not scaled (1:1) and too tiny to see comfortably. However, if I build
--with-pgtk, they are scaled 2:1, as I expect at such DPI.

Is it possible, and which knob do I need to turn, to get proper fringe
bitmap scaling on the GTK build?