[lldb][nfc] Mark function as const (#76974)

This function has no mutable behavior

Author: felipepiovezan

lldb/source/Plugins/SymbolFile/DWARF/DebugNamesDWARFIndex.cpp

@@ -48,7 +48,7 @@ DebugNamesDWARFIndex::GetUnits(const DebugNames &debug_names) {
 }
 
 std::optional<DIERef>
-DebugNamesDWARFIndex::ToDIERef(const DebugNames::Entry &entry) {
+DebugNamesDWARFIndex::ToDIERef(const DebugNames::Entry &entry) const {
   // Look for a DWARF unit offset (CU offset or local TU offset) as they are
   // both offsets into the .debug_info section.
   std::optional<uint64_t> unit_offset = entry.getCUOffset();

lldb/source/Plugins/SymbolFile/DWARF/DebugNamesDWARFIndex.h

@@ -79,7 +79,7 @@ class DebugNamesDWARFIndex : public DWARFIndex {
   std::unique_ptr<DebugNames> m_debug_names_up;
   ManualDWARFIndex m_fallback;
 
-  std::optional<DIERef> ToDIERef(const DebugNames::Entry &entry);
+  std::optional<DIERef> ToDIERef(const DebugNames::Entry &entry) const;
   bool ProcessEntry(const DebugNames::Entry &entry,
                     llvm::function_ref<bool(DWARFDIE die)> callback);