xargs: Prevent overflow in linelen calculation if nargs is large.

[des]

Summary

MFC after: 1 week
Sponsored by: Klara, Inc.

[jlduran]

Nice catch! Thank you!
Just a few minor suggestions in the tests.

usr.bin/xargs/tests/regress.n2147483647.out

2

This file needs to be included in usr.bin/xargs/tests/Makefile

usr.bin/xargs/tests/regress.sh

3

This needs to be bumped (+1).

[jlduran]

For some reason this patch is not working for me, It works fine on macOS. I'll take a closer look later.

[jlduran]

usr.bin/xargs/xargs.c

261

@des, sorry to insist, but I had to malloc -> calloc in order to get your test passing. Maybe I'm missing something here.

[markj]

I reverted the addition of the regression test since it triggers OOM kills in ci.freebsd.org and in my local testing environment. The problem is that the test triggers an allocation of 16GB when jemalloc debugging is enabled, and most environments don't have that much RAM available.

Is there any need to allow values for -n larger than ARG_MAX?