Introduce "optimized_out" oddball marker for compilers.

src/objects-debug.cc

Index: src/objects-debug.cc
diff --git a/src/objects-debug.cc b/src/objects-debug.cc
index 69042f0191e1b41d1df133fd78eda9282b50a2c7..0be32b62906186b40e685cea218f4b54106ae4e7 100644
--- a/src/objects-debug.cc
+++ b/src/objects-debug.cc
@@ -619,7 +619,7 @@ void Oddball::OddballVerify() {
     CHECK(number->IsSmi());
     int value = Smi::cast(number)->value();
     // Hidden oddballs have negative smis.
-    const int kLeastHiddenOddballNumber = -5;
+    const int kLeastHiddenOddballNumber = -6;
     CHECK_LE(value, 1);
     CHECK(value >= kLeastHiddenOddballNumber);
   }
@@ -642,6 +642,8 @@ void Oddball::OddballVerify() {
     CHECK(this == heap->termination_exception());
   } else if (map() == heap->exception_map()) {
     CHECK(this == heap->exception());
+  } else if (map() == heap->optimized_out_map()) {
+    CHECK(this == heap->optimized_out());
   } else {
     UNREACHABLE();
   }