[turbofan] Introduce explicit loop exits markers.

src/compiler/typer.cc

Index: src/compiler/typer.cc
diff --git a/src/compiler/typer.cc b/src/compiler/typer.cc
index 9ae1005f532634c63ac26b613968821d284124af..3ec223bf068ace17be13ac74195bd1046de1702a 100644
--- a/src/compiler/typer.cc
+++ b/src/compiler/typer.cc
@@ -713,6 +713,20 @@ Type* Typer::Visitor::TypeEffectPhi(Node* node) {
   return nullptr;
 }
 
+Type* Typer::Visitor::TypeLoopExit(Node* node) {
+  UNREACHABLE();
+  return nullptr;
+}
+
+Type* Typer::Visitor::TypeLoopExitMarker(Node* node) {
+  return Operand(node, 0);
+}
+
+Type* Typer::Visitor::TypeLoopExitEffect(Node* node) {
+  UNREACHABLE();
+  return nullptr;
+}
+
 Type* Typer::Visitor::TypeCheckpoint(Node* node) {
   UNREACHABLE();
   return nullptr;