Rotate GDM login screen

[白い熊 <help-guix_gnu.org@sumou.com>]

Hello:

I'm running Guix System on GPD Pocket 3 - it's a neat little device. Its 
screen is rotated anti-clockwise by 90 degrees by default, so to be 
usable it must be rotated by 90 to be used. This is easily achievable 
via appropriate kernel argument in system.scm, it rotates it once logged 
in.

However the GDM login screen itself is still rotated to the left - an 
ignorable nuisance. Anyhow for Debian-based systems, I've found the 
solution at:
https://www.reddit.com/r/GPDPocket/comments/s9ka7g/my_gpd_pocket_3_linux_setup/

via /etc/X11/xorg.conf.d/01-monitor.conf:

Section "Monitor"
     Identifier "DSI-1"
     Option "Rotate" "right"
EndSection

So, along the lines of solving the GDM screen using proper CJK/Japanese 
fonts in
https://lists.gnu.org/archive/html/help-guix/2022-05/msg00123.html

by using (extra-special-file in system.cfg to construct 
/var/lib/gdm/.config/fontconfig/fonts.conf what would be the similar 
file root to specify this config in an (extra-special-file statement, so 
that it'd be picked up on login and GDM would be properly rotated?

As a side note - and might be associated with this - can a small 
resolution be specified for just the GDM login screen - because on this 
computer the screen is tiny, the resolution big and thus the GDM login 
screen is with super tiny font everywhere.

Many thanks for help.
-- 
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白い熊
ShiroiKuma