ld_so/dso: don't use object's private ReadError; panic on unsupported reloc

The pinned object rev (da78133) makes the ReadError trait private AND
object::read::Error non-constructible (pub(crate) field), so the two
unsupported-relocation-type arms in static_relocate/lazy_relocate had no public
way to build an object::Error via None::<()>.read_error(msg)? (E0603 + 2x E0599).

An unsupported relocation type means the DSO cannot be loaded by this relibc
build — a fatal, unrecoverable link condition — so abort with the same message
via panic! and drop the private ReadError import. If graceful Err propagation is
preferred, the alternative is to revert the object pin to a rev where ReadError
is public. Surfaced by build-redbear.sh --check-sweep.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/ld_so/dso.rs

@@ -9,7 +9,6 @@ use object::{
             Dyn as _, GnuHashTable, HashTable as SysVHashTable, ProgramHeader as _,
             Rel as _, Rela as _, Sym as _, Version, VersionTable,
         },
-        ReadError,
     },
 };
 
@@ -1130,10 +1129,14 @@ impl DSO {
                 self.do_tlsdesc_reloc(reloc, ptr.cast::<usize>(), global_scope)
             }
             _ => {
-                None::<()>.read_error(concat!(
+                // object's ReadError/Error are private in the pinned object rev,
+                // so object::Error cannot be constructed here. An unsupported
+                // relocation type means this DSO cannot be loaded by this relibc
+                // build — a fatal, unrecoverable condition, so abort with it.
+                panic!(concat!(
                     "static_relocate: unsupported relocation type",
                     " (this DSO cannot be loaded by this relibc build)"
-                ))?;
+                ));
             }
         }
 
@@ -1208,11 +1211,11 @@ impl DSO {
                 }
 
                 _ => {
-                    None::<()>.read_error(concat!(
+                    panic!(concat!(
                         "lazy_relocate: unsupported relocation type with \
                          non-Lazy resolve (DSO cannot be loaded by this \
                          relibc build)"
-                    ))?;
+                    ));
                 }
             }
         }