Let's not leak details from src/shared and src/libsystemd into
src/basic, even though you can't actually do anything useful with
just forward declarations from src/shared.
The sd-forward.h header is put in src/libsystemd/sd-common as we
don't have a directory for shared internal headers for libsystemd
yet.
Let's also rename forward.h to basic-forward.h to keep things
self-explanatory.
To make sure everything still compiles, we add a preliminary include
of forward.h to tests.h to make sure it is included in every test source
file. We'll clean up the tests.h includes in a later commit.
We also add a <errno.h> include to errno-list.h to keep test-errno-list.c
compiling. It'll be removed again when we clean up includes in src/basic.
Split out of #37344.
Inspired by https://bugzilla.redhat.com/show_bug.cgi?id=1929936.
This is similar to test-nss-hosts, but does users, groups, uid, gids.
Functions tested are:
_nss_*_getpwnam_r
_nss_*_getgrnam_r
_nss_*_getpwgid_r
_nss_*_getgrgid_r
Other entry points should be tested too, but it's not relevant to the bug
I was investigating, so I'm leaving that for later ;)