[wasm] Backoff implementation for F64Trunc using std::trunc.

src/assembler.h

Index: src/assembler.h
diff --git a/src/assembler.h b/src/assembler.h
index e65209b0fe773c84620226e73040e0bcbedd31ac..57c6109f892be66a0153222e6644f807ce5a2d35 100644
--- a/src/assembler.h
+++ b/src/assembler.h
@@ -907,6 +907,8 @@ class ExternalReference BASE_EMBEDDED {
   static ExternalReference new_deoptimizer_function(Isolate* isolate);
   static ExternalReference compute_output_frames_function(Isolate* isolate);
 
+  static ExternalReference trunc64_wrapper_function(Isolate* isolate);
+
   // Log support.
   static ExternalReference log_enter_external_function(Isolate* isolate);
   static ExternalReference log_leave_external_function(Isolate* isolate);