bug#42006: Installing font-dejavu breaks other fonts

[Leo Famulari]

Since my last full upgrade on June 9 2020, I found that if I have
font-dejavu installed in my profile, my terminal (rxvt-unicode) no
longer finds the font selected in my ~/.Xresources file.

I'm using Guix on Debian, and all the packages involved are installed by
Guix. They are rxvt-unicode, font-anonymous-pro, and font-dejavu.

I strace-d the terminal startup.

In the good case, it reads and loads a bunch font-related things before
it finally loads my specified font from its symlink in
'~/.guix-profile/share/fonts'.

In the bad case, this work is cut short before it loads the DejaVu font
directly from the store.

I've attached excerpts of these traces as 'good.log' and 'bad.log'.

Here is a manifest to test the effect:

------
(specifications->manifest
 '(glibc-utf8-locales"
   "rxvt-unicode"
   "font-anonymous-pro"
   "font-gnu-unifont:pcf"
   "font-gnu-unifont:psf"
   "font-gnu-unifont:bin"
   "font-gnu-unifont"
   "font-dejavu" ; comment this package to toggle the bug on and off
))
------

And the ~/.Xresources file:

------
Urxvt*scrollBar: false
URxvt*font:     xft:Anonymous Pro:pixelsize=13:antialiasing=true \
                xft:unifont:style=Medium:antialias=false:size=16
Xft.hinting:    1
Xft.hintstyle:  hintfull
!
! this is a comment
!urxvt*foreground:White
!urxvt*background:Black

urxvt*foreground:Black
urxvt*background:White
------

good.log
Description: Text document

bad.log
Description: Text document