[lld-macho] Process OSO prefix only textually in both input and output (#152063)

The processing of `-oso_prefix` uses `llvm::sys::fs::real_path` from the
user value, but it is later tried to be matched with the result of
`make_absolute`. While `real_path` resolves special symbols like `.`,
`..` and `~`, and resolves symlinks along the path, `make_absolute` does
neither, causing an incompatibility in some situations.

In macOS, temporary directories would normally be reported as
`/var/folders/<random>`, but `/var` is in fact a symlink to
`private/var`. If own is working on a temporary directory and uses
`-oso_prefix .`, it will be expanded to `/private/var/folder/<random>`,
while `make_absolute` will expand to `/var/folder/<random>` instead, and
`-oso_prefix` will fail to remove the prefix from the `N_OSO` entries,
leaving absolute paths to the temporary directory in the resulting file.
This would happen in any situation in which the working directory
includes a symlink, not only in temporary directories.

One can change the usage of `make_absolute` to use `real_path` as well,
but `real_path` will mean checking the file system for each `N_OSO`
entry. The other solution is stop using `real_path` when processing
`-oso_prefix` and manually expand an input of `.` like `make_absolute`
will do.

This second option is the one implemented here, since it is the closest
to the visible behaviour of ld64 (like the removed comment notes), so it
is the better one for compatibility. This means that a test that checked
the usage of the tilde as `-oso_prefix` needs to be removed (since it
was done by using `real_path`), and two new tests are provided checking
that symlinks do not affect the result. The second test checks a change
in behaviour, in which if one provides the input files with a prefix of
`./`, even when using `-oso_prefix .` because the matching is textual,
the `./` prefix will stay in the `N_OSO` entries. This matches the
observed behaviour of ld64.

0 files changed, 0 insertions, 0 deletions