Avoid declaring a fake dependency edge
When we're producing an rlib, we do not need anything more than an rmeta file
for each of our dependencies (this is indeed utilized by Cargo for pipelining).
Previously, we were still storing the paths of possible rlib/dylib crates, which
meant that they could still plausibly be accessed. With -Zbinary-dep-depinfo,
that meant that Cargo thought that rustc was using both the rlib and an (earlier
emitted) rmeta, and so needed a recompile, as the rlib may have finished writing
*after* compilation started (for more detail, see issue 68149).
This commit changes metadata loading to not store the filepaths of dylib/rlib if
we're going to end up creating an rlib only.
Fixes#68149.
462fc37fa8