bin/56584: "grep -D skip" fails to skip FIFOs

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

>Number:         56584
>Category:       bin
>Synopsis:       "grep -D skip" fails to skip fifos
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Dec 27 14:25:00 +0000 2021
>Originator:     Andreas Gustafsson
>Release:        NetBSD 9.2; also -current
>Organization:
>Environment:
System: NetBSD
Architecture: x86_64
Machine: amd64
>Description:

The grep(1) man page states:

       -D ACTION, --devices=ACTION
              If an input file is a device, FIFO or socket, use ACTION to
              process it.  By default, ACTION is read, which means that
              devices are read just as if they were ordinary files.  If ACTION
              is skip, devices are silently skipped.

but when "grep -D skip" encounters a FIFO, it is read rather than skipped.

>How-To-Repeat:

# mkfifo fifo
# grep -D skip fifo

>Fix: