Rely on information provided by /proc/*/stat and /sys/dev/char for resolving
the controlling tty for the display server, instead of trying to access the
tty device in /dev (which may not be accessible for example due to
PrivateDevices=yes).
The tool deals with any kind of 128bit id, not just uuid, and by default
we display just a series of hex chars, hence let's not claim everything
was a "uuid", but just generically say "id"
Previously there was a weird asymmetry: initially we'd resolve the
specified prefix path when chasing symlinks together with the actual
path we were supposed to cover, except when we hit an absolute symlink
where we'd use the root as it was. Let's unify handling here: the prefix
path is never resolved, and always left as it is.
This in particular fixes issues with symlinks in the prefix path, as
that confused the check that made sure we never left the root directory.
Fixes: #14634
Replaces: #14635
```
ninja -C build
ninja: Entering directory `build'
[29/101] Generating systemd_boot.so with a custom command.
FAILED: src/boot/efi/systemd_boot.so
/usr/bin/ld -o src/boot/efi/systemd_boot.so -T /usr/lib64/gnuefi/elf_x64_efi.lds -shared -Bsymbolic -nostdlib -znocombreloc -L /usr/lib64 /usr/lib64/gnuefi/crt0-efi-x64.o src/boot/efi/disk.c.o src/boot/efi/graphics.c.o src/boot/efi/measure.c.o src/boot/efi/pe.c.o src/boot/efi/util.c.o src/boot/efi/boot.c.o src/boot/efi/console.c.o src/boot/efi/crc32.c.o src/boot/efi/random-seed.c.o src/boot/efi/sha256.c.o src/boot/efi/shim.c.o -lefi -lgnuefi /usr/lib/gcc/x86_64-redhat-linux/10/libgcc.a
/usr/bin/ld: src/boot/efi/graphics.c.o:/home/sus/tt/systemd/build/../src/boot/efi/util.h:58: multiple definition of `loader_guid'; src/boot/efi/disk.c.o:/home/sus/tt/systemd/build/../src/boot/efi/util.h:58: first defined here
/usr/bin/ld: src/boot/efi/pe.c.o:/home/sus/tt/systemd/build/../src/boot/efi/util.h:58: multiple definition of `loader_guid'; src/boot/efi/disk.c.o:/home/sus/tt/systemd/build/../src/boot/efi/util.h:58: first defined here
/usr/bin/ld: src/boot/efi/util.c.o:/home/sus/tt/systemd/build/../src/boot/efi/util.h:58: multiple definition of `loader_guid'; src/boot/efi/disk.c.o:/home/sus/tt/systemd/build/../src/boot/efi/util.h:58: first defined here
/usr/bin/ld: src/boot/efi/boot.c.o:/home/sus/tt/systemd/build/../src/boot/efi/util.h:58: multiple definition of `loader_guid'; src/boot/efi/disk.c.o:/home/sus/tt/systemd/build/../src/boot/efi/util.h:58: first defined here
/usr/bin/ld: src/boot/efi/console.c.o:/home/sus/tt/systemd/build/../src/boot/efi/util.h:58: multiple definition of `loader_guid'; src/boot/efi/disk.c.o:/home/sus/tt/systemd/build/../src/boot/efi/util.h:58: first defined here
/usr/bin/ld: src/boot/efi/random-seed.c.o:/home/sus/tt/systemd/build/../src/boot/efi/util.h:58: multiple definition of `loader_guid'; src/boot/efi/disk.c.o:/home/sus/tt/systemd/build/../src/boot/efi/util.h:58: first defined here
/usr/bin/ld: src/boot/efi/shim.c.o:/home/sus/tt/systemd/build/../src/boot/efi/util.h:58: multiple definition of `loader_guid'; src/boot/efi/disk.c.o:/home/sus/tt/systemd/build/../src/boot/efi/util.h:58: first defined here
[31/101] Generating stub.c.o with a custom command.
ninja: build stopped: subcommand failed.
make: *** [Makefile:2: all] Error 1
```
