[turbofan] Drop V8_TURBOFAN_BACKEND and V8_TURBOFAN_TARGET defines.

src/compiler/pipeline.cc

Index: src/compiler/pipeline.cc
diff --git a/src/compiler/pipeline.cc b/src/compiler/pipeline.cc
index c1e2eb663e0a0d4fccfaf19eb00c42e7f356a4dd..a1b82318c2753ec883accf8abd7d425643a42fcc 100644
--- a/src/compiler/pipeline.cc
+++ b/src/compiler/pipeline.cc
@@ -1076,9 +1076,6 @@ Handle<Code> Pipeline::GenerateCode() {
     GraphReplayPrinter::PrintReplay(data.graph());
   }
 
-  // Bailout here in case target architecture is not supported.
-  if (!SupportedTarget()) return Handle<Code>::null();
-
   base::SmartPointer<Typer> typer;
   if (info()->is_typing_enabled()) {
     // Type the graph.
@@ -1203,7 +1200,6 @@ Handle<Code> Pipeline::ScheduleAndGenerateCode(
   PipelineData* data = this->data_;
 
   DCHECK_NOT_NULL(data->graph());
-  CHECK(SupportedBackend());
 
   if (data->schedule() == nullptr) Run<ComputeSchedulePhase>();
   TraceSchedule(data->info(), data->schedule());