Fix a build error for use_custom_libcxx=false use_sysroot=false

This reverts part of crrev.com/c/2413252 since std::unique_ptr does
not satisfy is_standard_layout; and is_standard_layout is needed
to use offsetof:

 error: offset of on non-standard-layout type [-Werror,-Winvalid-offsetof]

Fixed: v8:12721
Change-Id: Ifbb1235fc3b8d1d855d41a226117fed88c506078
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3540141Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79597}

src/deoptimizer/deoptimizer.cc

@@ -95,7 +95,7 @@ class FrameWriter {
                            const char* debug_hint = "") {
     Object obj = iterator->GetRawValue();
     PushRawObject(obj, debug_hint);
-    if (trace_scope_) {
+    if (trace_scope_ != nullptr) {
       PrintF(trace_scope_->file(), " (input #%d)\n", iterator.input_index());
     }
     deoptimizer_->QueueValueForMaterialization(output_address(top_offset_), obj,
@@ -580,6 +580,7 @@ Handle<Code> Deoptimizer::compiled_code() const {
 Deoptimizer::~Deoptimizer() {
   DCHECK(input_ == nullptr && output_ == nullptr);
   DCHECK_NULL(disallow_garbage_collection_);
+  delete trace_scope_;
 }
 
 void Deoptimizer::DeleteFrameDescriptions() {

src/deoptimizer/deoptimizer.h

@@ -182,11 +182,11 @@ class Deoptimizer : public Malloced {
   Code FindDeoptimizingCode(Address addr);
 
   // Tracing.
-  bool tracing_enabled() const { return static_cast<bool>(trace_scope_); }
+  bool tracing_enabled() const { return trace_scope_ != nullptr; }
   bool verbose_tracing_enabled() const {
-    return FLAG_trace_deopt_verbose && trace_scope_;
+    return FLAG_trace_deopt_verbose && tracing_enabled();
   }
-  CodeTracer::Scope* trace_scope() const { return trace_scope_.get(); }
+  CodeTracer::Scope* trace_scope() const { return trace_scope_; }
   CodeTracer::Scope* verbose_trace_scope() const {
     return FLAG_trace_deopt_verbose ? trace_scope() : nullptr;
   }
@@ -239,7 +239,9 @@ class Deoptimizer : public Malloced {
   DisallowGarbageCollection* disallow_garbage_collection_;
 #endif  // DEBUG
 
-  std::unique_ptr<CodeTracer::Scope> trace_scope_;
+  // Note: This is intentionally not a unique_ptr s.t. the Deoptimizer
+  // satisfies is_standard_layout, needed for offsetof().
+  CodeTracer::Scope* const trace_scope_;
 
   friend class DeoptimizedFrameInfo;
   friend class FrameDescription;