[lldb][SymbolFileDWARF][NFC] Remove unnecessary calls to GetDWARFDecl…

…Context (llvm#74523)

The function FindDefinitionTypeForDWARFDeclContext loops over all DIEs
corresponding to types with a certain name and compares the context of
each found DIE with the context of a target DIE. However, the target DIE
never changes throughout this search, and yet we recompute its
DeclContext on every iteration of the search. This is wasteful because
the method is not exactly free (see
DWARFDebugInfoEntry::GetDWARFDeclContextStatic).

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

@@ -3120,7 +3120,8 @@ SymbolFileDWARF::FindDefinitionTypeForDWARFDeclContext(const DWARFDIE &die) {
         template_params = dwarf_ast->GetDIEClassTemplateParams(die);
     }
 
-    m_index->GetTypes(GetDWARFDeclContext(die), [&](DWARFDIE type_die) {
+    const DWARFDeclContext die_dwarf_decl_ctx = GetDWARFDeclContext(die);
+    m_index->GetTypes(die_dwarf_decl_ctx, [&](DWARFDIE type_die) {
       // Make sure type_die's language matches the type system we are
       // looking for. We don't want to find a "Foo" type from Java if we
       // are looking for a "Foo" type for C, C++, ObjC, or ObjC++.
@@ -3184,7 +3185,7 @@ SymbolFileDWARF::FindDefinitionTypeForDWARFDeclContext(const DWARFDIE &die) {
       }
 
       // Make sure the decl contexts match all the way up
-      if (GetDWARFDeclContext(die) != type_dwarf_decl_ctx)
+      if (die_dwarf_decl_ctx != type_dwarf_decl_ctx)
         return true;
 
       Type *resolved_type = ResolveType(type_die, false);