[turbofan] Avoid using the typer's types in representation inference for phis.

src/compiler/representation-change.cc

Index: src/compiler/representation-change.cc
diff --git a/src/compiler/representation-change.cc b/src/compiler/representation-change.cc
index 01ca8d3732f6f13883173e5ce89a2c0035bee343..5dab60f6a32bd06a101d7e6e380f184498b7115c 100644
--- a/src/compiler/representation-change.cc
+++ b/src/compiler/representation-change.cc
@@ -64,7 +64,7 @@ Truncation::TruncationKind Truncation::Generalize(TruncationKind rep1,
     return TruncationKind::kFloat64;
   }
   // All other combinations are illegal.
-  FATAL("Tried to combine incompatible representations");
+  FATAL("Tried to combine incompatible truncations");
   return TruncationKind::kNone;
 }