bin/60357: diff3(1): tests are failing since BSD diff import

["campbell+netbsd%mumble.net@localhost via gnats" <gnats-admin%NetBSD.org@localhost>]

>Number:         60357
>Category:       bin
>Synopsis:       diff3(1): tests are failing since BSD diff import
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Jun 23 17:15:00 +0000 2026
>Originator:     Taylor R Campbell
>Release:        current
>Organization:
The NetBSD Diff (but NotBSDiff) Foundation
>Environment:
>Description:
Happening intermittently on various platforms, such as riscv:
https://releng.netbsd.org/b5reports/riscv-riscv64/2026/2026.06.15.06.28.55/test.html#usr.bin_diff3_t_diff3_diff3_A

Test case: usr.bin/diff3/t_diff3/diff3_A

Duration: 1.431946 seconds
Termination reason

FAILED: atf-check failed; see the output of the test for details
Standard output stream

Executing command [ diff3 -A -L 1 -L 2 -L 3 /usr/tests/usr.bin/diff3/1.txt /usr/tests/usr.bin/diff3/2.txt /usr/tests/usr.bin/diff3/3.txt ]

Standard error stream

Fail: incorrect exit status: 2, expected: 1
stdout:

stderr:
diff3: kevent2: No such process

>How-To-Repeat:
cd /usr/tests/usr.bin/diff3 && atf-run | atf-report
>Fix:
Yes, please!