[M] Change in flashrom[master]: tests: Emulate multithreading environment for unit tests

[Anastasia Klimchuk (Code Review)]

Attention is currently required from: Thomas Heijligen, Anastasia Klimchuk.

Hello build bot (Jenkins), Thomas Heijligen, Peter Marheine,

I'd like you to reexamine a change. Please visit

https://review.coreboot.org/c/flashrom/+/74157

to look at the new patch set (#4).

Change subject: tests: Emulate multithreading environment for unit tests
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tests: Emulate multithreading environment for unit tests

The main purpose of this patch is to run unit tests on BSD family
of OSes. The root cause is `fileno` syscall which is a macro that
can be expanded to either a function call (for multi-threaded
environment) or to inline code (for single-threaded environment).
Said inline code accesses private field of file descriptor, and
this construction is impossible to mock in unit tests. Multi-
threaded environment has `fileno` as a function, which can be
mocked in unit tests.

On other OSes the patch just creates a thread which is doing nothing.
We avoid adding pre-processor conditionals since the cost is small.

Tested on
FreeBSD 13.1-RELEASE-p6 GENERIC amd64
NetBSD 9.2 (GENERIC) amd64
OpenBSD 7.2 GENERIC#7 amd64
[WIP] DragonFly v6.4.0-RELEASE x86_64
Ubuntu 22.04.1 x86_64

Change-Id: I3d65c125183e60037ad07b9d54b8fffdece5a4e8
Signed-off-by: Anastasia Klimchuk 
---
M tests/meson.build
M tests/tests.c
2 files changed, 51 insertions(+), 12 deletions(-)

git pull ssh://review.coreboot.org:29418/flashrom refs/changes/57/74157/4