kern/56780: lib/libc/sys/t_mmap:mmap_err test case fails randomly

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

>Number:         56780
>Category:       kern
>Synopsis:       lib/libc/sys/t_mmap:mmap_err test case fails randomly
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Apr 05 13:25:00 +0000 2022
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current
>Organization:

>Environment:
System: NetBSD
Architecture: i386
Machine: i386
>Description:

The TNF i386 testbed testbed just reported a failure of the
lib/libc/sys/t_mmap:mmap_err test case:

  http://releng.netbsd.org/b5reports/i386/2022/2022.04.02.22.15.57/test.html#lib_libc_sys_t_mmap_mmap_err

It fails with the message

  FAILED: /tmp/build/2022.04.02.22.15.57-i386/src/tests/lib/libc/sys/t_mmap.c:231: errno == EINVAL not met

I committed a change to make the test print the actual errno value at
the time of failure, and it's 9 (EBADF).

The testbed logs show sporadic failures of this test case going back
at least to 2018.

>How-To-Repeat:

# cd /usr/tests/lib/libc/sys
# while ./t_mmap map_err; do true; done

>Fix: