[lldb] Restore Swift IsSymbolARuntimeThunk override (#2917)

The swift override of `IsSymbolARuntimeThunk` was unintentionally removed in #536. This restores it.

rdar://65681037

Author: kastiglione

lldb/source/Plugins/LanguageRuntime/Swift/SwiftLanguageRuntime.h

@@ -123,6 +123,8 @@ class SwiftLanguageRuntime : public LanguageRuntime {
 
   void ModulesDidLoad(const ModuleList &module_list) override;
 
+  bool IsSymbolARuntimeThunk(const Symbol &symbol) override;
+
   /// Mangling support.
   /// \{
   /// Use these passthrough functions rather than calling into Swift directly,

lldb/source/Plugins/LanguageRuntime/Swift/SwiftLanguageRuntimeNames.cpp

@@ -596,6 +596,15 @@ static lldb::ThreadPlanSP GetStepThroughTrampolinePlan(Thread &thread,
   return new_thread_plan_sp;
 }
 
+bool SwiftLanguageRuntime::IsSymbolARuntimeThunk(const Symbol &symbol) {
+  llvm::StringRef symbol_name =
+      symbol.GetMangled().GetMangledName().GetStringRef();
+  if (symbol_name.empty())
+    return false;
+  swift::Demangle::Context demangle_ctx;
+  return demangle_ctx.isThunkSymbol(symbol_name);
+}
+
 bool SwiftLanguageRuntime::IsSwiftMangledName(llvm::StringRef name) {
   return swift::Demangle::isSwiftSymbol(name);
 }