bug#44701: 28.0.50; [feature/native-comp] Use file-truename when building eln path hash

[Tad]

It appears that `comp-el-to-eln-filename` uses `expand-file-name` to
determine the absolute filename to
hash. When the filename is a symlink, this results in a cache miss
depending on which path is loaded.

`file-truename' would be the equivalent to `(expand-file-name name
nil)`, except that it would resolve to a
single canonical path (in the absence of hardlinks, which is pathological).

If I may ask, what is the purpose behind the path component of the
hash? I would think a content hash
would suffice to disambiguate files in the .el<->.eln bijection.

Thanks,
Tad