Spack comes to a crawl post-install of nvhpc, which is partly thanks to
this post install hook which has a lot of redundancy, and isn't correct.
1. There's no need to store "type" because that _is_ "mode".
2. There are more file types than "symlink", "dir", "file".
3. Don't checksum device type things
4. Don't run 3 stat calls (exists, stat, isdir/islink), but one lstat
call
5. Don't read entire files into memory
I also don't know why `spack.crypto` wasn't used for checksumming, but I
guess it's too late for that now. Finally md5 would've been the faster
algorithm, which would've been fine given that a non cryptographicall
checksum was used anyways.
c85877566f