SimpleProject: Teach maybe_strip_elf_file to check for symlinks

If a file is a symlink we don't want to actually strip it and lose the
link. Moreover, is_file() can raise a PermissionError for a symlink to a
path we can't access when building on the host (e.g. if you create an
extra-files tree with an absolute symlink to somewhere in /root)

pycheribuild/projects/simple_project.py

@@ -1164,7 +1164,10 @@ def __run_process_with_filtered_output(self, proc: subprocess.Popen, logfile: "O
     def maybe_strip_elf_file(self, file: Path, *, output_path: "Optional[Path]" = None,
                              print_verbose_only=True) -> bool:
         """Runs llvm-strip on the file if it is an ELF file and it is safe to do so."""
-        if not file.is_file():
+        # NB: Must check if it's a symlink first; if it refers to a path we
+        # don't have permission to stat on the host (e.g. a symlink into /root)
+        # then is_file() will raise a PermissionError.
+        if file.is_symlink() or not file.is_file():
             return False
         try:
             with file.open("rb") as f: