Regression since Racket 8.5: fonts are required to build successfully.

We are compiling Racket in a minimalist container (Void Linux x86_64 glibc), and Racket 8.4 builds fine without any true-type fonts installed.
However, since 8.5 (and also in snapshot 8.5.0.8), raco setup fails when no fonts are found:

raco setup: error: during building docs for <pkgs>/racket-doc/scribblings/guide/guide.scrbl                                                                     
raco setup:   draw-polygon in dc<%>: drawing context is not ok: (wrapper-object:bitmap-dc% ...)                                                                 
raco setup:     context...:                                                     
raco setup:      .../private/arrow-higher-order.rkt:375:33: ...row-higher-order.rkt:375:33                                                                      
raco setup:      /destdir/racket-8.6/usr/share/racket/pkgs/pict-lib/pict/private/utils.rkt:653:9                                                                
raco setup:      /destdir/racket-8.6/usr/share/racket/pkgs/pict-lib/pict/private/pict.rkt:1805:6: loop                                                          
raco setup:      [repeats 1 more time]                                          
raco setup:      /destdir/racket-8.6/usr/share/racket/pkgs/pict-lib/pict/private/pict.rkt:1969:0: convert-pict/bytes                                            
raco setup:      /destdir/racket-8.6/usr/share/racket/pkgs/pict-lib/pict/private/pict.rkt:1919:0: convert-pict                                                  
raco setup:      /destdir/racket-8.6/usr/share/racket/pkgs/scribble-lib/scribble/html-render.rkt:1261:4: render-content method in render-mixin                  
raco setup:      /destdir/racket-8.6/usr/share/racket/pkgs/scribble-lib/scribble/base-render.rkt:974:4: render-content method in render%                        
raco setup:      /destdir/racket-8.6/usr/share/racket/pkgs/scribble-lib/scribble/html-render.rkt:1207:4: do-render-paragraph method in render-mixin             
raco setup:      /destdir/racket-8.6/usr/share/racket/pkgs/scribble-lib/scribble/base-render.rkt:969:4: render-nested-flow method in render
raco setup:      /destdir/racket-8.6/usr/share/racket/pkgs/scribble-lib/scribble/html-render.rkt:1775:4: render-nested-flow method in render-mixin              
raco setup:      /destdir/racket-8.6/usr/share/racket/pkgs/scribble-lib/scribble/html-render.rkt:1194:6: loop                                                   
raco setup:      [repeats 2 more times]                                         
raco setup:      /destdir/racket-8.6/usr/share/racket/pkgs/scribble-lib/scribble/html-render.rkt:1118:4: render-part-content method in render-mixin             
raco setup:      /destdir/racket-8.6/usr/share/racket/pkgs/scribble-lib/scribble/html-render.rkt:1184:14: loop                                                  
raco setup:      /destdir/racket-8.6/usr/share/racket/pkgs/scribble-lib/scribble/html-render.rkt:1118:4: render-part-content method in render-mixin             
raco setup:      ...                                                            
raco setup:                                                                     
failed          

Installing e.g. the liberation-ttf fonts fixes this problem.

If fonts are required for building, it would be good to get a better error message. Else, this may be a regression from 8.4

Reproduce the failure with raco setup in a minimalist environment without fonts, focusing on <pkgs>/racket-doc/scribblings/guide/guide.scrbl. Read the reported paths in pict/private/utils.rkt, pict/private/pict.rkt, and the Scribble renderers to determine whether missing fonts are expected. Done means either the build no longer fails without fonts or it reports the requirement clearly.