bin/55914: Set extraction fails with "Interrupted system call"

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

>Number:         55914
>Category:       bin
>Synopsis:       Set extraction fails with "Interrupted system call"
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Jan 07 09:20:00 +0000 2021
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current, source date >= 2021.01.06.04.43.14
>Organization:
>Environment:
System: NetBSD
Architecture: sparc
Machine: sparc
>Description:

On the TNF sparc testbed, installation is failing at the set
extraction stage, with the error message

  progress: writing 8192 bytes to output pipe: Interrupted system call

since this commit:

  2021.01.06.04.43.14 lukem src/usr.bin/ftp/ftp.c 1.171
  2021.01.06.04.43.14 lukem src/usr.bin/ftp/progressbar.c 1.24
  2021.01.06.04.43.14 lukem src/usr.bin/ftp/progressbar.h 1.9
  2021.01.06.04.43.14 lukem src/usr.bin/ftp/ssl.c 1.9
  2021.01.06.04.43.14 lukem src/usr.bin/ftp/version.h 1.92

Logs:

  http://releng.netbsd.org/b5reports/sparc/commits-2021.01.html#2021.01.06.04.43.14

There have also been random install failures on amd64:

  http://releng.netbsd.org/b5reports/amd64/commits-2021.01.html#2021.01.06.14.07.43

  https://www.gson.org/netbsd/bugs/build/amd64-baremetal/commits-2021.01.html#2021.01.06.20.38.09

>How-To-Repeat:

>Fix: