elf: relocate PT_INTERP (#42318)

Relocation of `PT_INTERP` in ELF files already happens to work from long to short path, thanks to generic binary relocation (i.e. find and replace). This PR improves it:

1. Adds logic to grow `PT_INTERP` strings through patchelf (which is only useful if the interpreter and rpath paths are the _only_ paths in the binary that need to be relocated)
2. Makes shrinking `PT_INTERP` cleaner. Before this PR when you would use Spack-built glibc as link dep, and relocate
executables using its dynamic linker, you'd end up with

   ```
   $ file exe
   exe: ELF 64-bit LSD pie executable, ..., interpreter /////////////////////////////////////////////////path/to/glibc/lib/ld-linux.so
   ```

   With this PR you get something sensible:

   ```
   $ file exe
   exe: ELF 64-bit LSD pie executable, ..., interpreter /path/to/glibc/lib/ld-linux.so
   ```

When Spack cannot modify the interpreter or rpath strings in-place, it errors out without modifying the file, and leaves both tasks to patchelf instead.

Also add type hints to `elf.py`.

0 files changed, 0 insertions, 0 deletions