misc/59815: Random build.sh -x failures involving libglx.a

[gson%gson.org@localhost (Andreas Gustafsson)]

>Number:         59815
>Category:       misc
>Synopsis:       Random build.sh -x failures involving libglx.a
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    misc-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Dec 03 12:05:00 +0000 2025
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current, source date 2025.12.03.08.26.10
>Organization:
  
>Environment:
System: NetBSD
Architecture: x86_64
Machine: amd64
>Description:

Building NetBSD-current/amd64 including xsrc using build.sh -x, I'm
seeing random build failures with errors like this:

  nbmake[13]: don't know how to make /dev/shm/build/2025.12.03.08.26.10-amd64/obj/external/mit/xorg/server/xorg-server/hw/xfree86/dixmods/glx/libglx.a. Stop

I'm bulding on a Linux host; I don't know if that makes a difference or not.
It doesn't happen on the TNF testbeds because they don't build with -x.

Logs:

  https://www.gson.org/netbsd/bugs/build/amd64/2025/2025.11.29.22.10.55/build.log.tail
  https://www.gson.org/netbsd/bugs/build/amd64/2025/2025.12.03.08.26.10/build.log.tail

>How-To-Repeat:

>Fix: