time_t is pathological: use %j + cast to print it.

Sponsored by: Netflix

sem_clockwait_np test: fix usage of ATF API

ATF_REQUIRE_ERRNO requires the given errno iff the given expression is
true. These test cases used it incorrectly, potentially allowing
sem_clockwait_np to succeed when it was expected to fail. Use separate
ATF calls to require failure and the expected errno.

MFC after: 1 week
Sponsored by: Dell EMC Isilon

sem test: move sem_clockwait_np tests into individual cases

Move these tests into individual test cases for all the usual reasons.
No functional change intended.

MFC after: 1 week
Sponsored by: Dell EMC Isilon

sem_clockwait_np test: relax time constraint on VMs

In a guest on a busy hypervisor, the time remaining after an
interrupted sleep could be much lower than other environments.
Relax the lower bound on VMs.

MFC after: 1 week
Sponsored by: Dell EMC Isilon

librt: tests: fix minor issues with higher WARNS

got_sigalrm is a global with external linkage and must therefore have a
previous extern declaration. There's no reason to maintain the status quo
there, so just make it static.

The result var is unused.

This part of the test has not been upstreamed, presumably because it exists
solely for sem_clockwait_np. We should perhaps consider moving it into its
own test file outside of ^/contrib/netbsd-tests, but this can happen later.

MFC after: 1 week

Add sem_clockwait_np()

This function allows the caller to specify the reference clock
and choose between absolute and relative mode. In relative mode,
the remaining time can be returned.

The API is similar to clock_nanosleep(3). Thanks to Ed Schouten
for that suggestion.

While I'm here, reduce the sleep time in the semaphore "child"
test to greatly reduce its runtime. Also add a reasonable timeout.

Reviewed by: ed (userland)
MFC after: 2 weeks
Relnotes: yes
Sponsored by: Dell EMC
Differential Revision: https://reviews.freebsd.org/D9656

Use cleanup routines to remove POSIX semaphores instead of just blindly
unlinking them at the beginning of the testcase

This is a lot more intelligent in cleaning up the semaphores if the testcase
fails before sem_unlink is called.

Contributed back as bin/51872 upstream.

Call sem_unlink on semaphores before attempting to create them

Due to the lack of uniqueness in the semaphore name, and the fact that the
tests don't have cleanup routines, an interrupted test can leave a semaphore
"laying around", causing all subsequent attempts to run the test to fail

I will file a NetBSD PR for this issue soon