Swiss Keyboard Layout in recent xorg ("AltGr doesn't work")

It took me a while to figure out what was going on, so I hope this can be useful to someone else...

In gentoo, you need to unmerge x11-misc/xkeyboard-config and emerge x11-misc/xkbdata instead. (I have xorg-x11 7.1)

Then your keyboard section in xorg.conf needs to look like this:

Section "InputDevice"
        Identifier      "Generic Keyboard"
        Driver          "kbd"
        Option          "XkbRules"      "xorg"
        Option          "XkbModel"      "pc105"
        Option          "XkbLayout"     "ch(fr)"
EndSection

fr_CH will not work. well, it sort of worked, but none of the AltGr combinations would work, regardless of what I tried with xmodmap, despite the keycode returned by xev being correct etc.