Revert "Disable kBssEntry LoadString sharpening."

Fix .bss GC root walking by registering the oat file
with the class loader's class table.

Also fix potentially outdated ObjPtr<> use in debug build.

This reverts commit b55fdbb30b3bc4e334c241153b98c0a6ea4a4a2b.

Test: m test-art-host
Bug: 32124939
Change-Id: I0b7e3b93cb53c7b22408aa10a04eaf5582c69ee8
diff --git a/compiler/optimizing/sharpening.cc b/compiler/optimizing/sharpening.cc
index df1b351..c1cfe8d 100644
--- a/compiler/optimizing/sharpening.cc
+++ b/compiler/optimizing/sharpening.cc
@@ -312,8 +312,7 @@
         desired_load_kind = HLoadString::LoadKind::kBootImageAddress;
         address = reinterpret_cast64<uint64_t>(string);
       } else {
-        // FIXME: Disabled because of BSS root visiting issues. Bug: 32124939
-        // desired_load_kind = HLoadString::LoadKind::kBssEntry;
+        desired_load_kind = HLoadString::LoadKind::kBssEntry;
       }
     }
   }