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

test/cctest/wasm/test-run-wasm.cc

Index: test/cctest/wasm/test-run-wasm.cc
diff --git a/test/cctest/wasm/test-run-wasm.cc b/test/cctest/wasm/test-run-wasm.cc
index 1d40e10048b02d79682bf43029075dddb326a0b8..66e8206627510b915480d2e5cc72391ea5bfd1d5 100644
--- a/test/cctest/wasm/test-run-wasm.cc
+++ b/test/cctest/wasm/test-run-wasm.cc
@@ -3006,14 +3006,6 @@ TEST(Run_Wasm_F64Ceil) {
 }
 
 
-TEST(Run_Wasm_F64Trunc) {
-  WasmRunner<double> r(MachineType::Float64());
-  BUILD(r, WASM_F64_TRUNC(WASM_GET_LOCAL(0)));
-
-  FOR_FLOAT64_INPUTS(i) { CheckDoubleEq(trunc(*i), r.Call(*i)); }
-}
-
-
 TEST(Run_Wasm_F64NearestInt) {
   WasmRunner<double> r(MachineType::Float64());
   BUILD(r, WASM_F64_NEARESTINT(WASM_GET_LOCAL(0)));
@@ -3023,6 +3015,12 @@ TEST(Run_Wasm_F64NearestInt) {
 
 #endif
 
+TEST(Run_Wasm_F64Trunc) {
+  WasmRunner<double> r(MachineType::Float64());
+  BUILD(r, WASM_F64_TRUNC(WASM_GET_LOCAL(0)));
+
+  FOR_FLOAT64_INPUTS(i) { CheckDoubleEq(trunc(*i), r.Call(*i)); }
+}
 
 TEST(Run_Wasm_F32Min) {
   WasmRunner<float> r(MachineType::Float32(), MachineType::Float32());