[turbofan] Implemented the optional Float32RoundTruncate operator.

src/compiler/x87/instruction-selector-x87.cc

Index: src/compiler/x87/instruction-selector-x87.cc
diff --git a/src/compiler/x87/instruction-selector-x87.cc b/src/compiler/x87/instruction-selector-x87.cc
index 0746300dcc1478916c5b1deeadc0329af7056a4d..52dfbff3eeaef46c79b682d8667a240d8d4b3dc2 100644
--- a/src/compiler/x87/instruction-selector-x87.cc
+++ b/src/compiler/x87/instruction-selector-x87.cc
@@ -858,6 +858,11 @@ void InstructionSelector::VisitFloat32RoundUp(Node* node) { UNREACHABLE(); }
 void InstructionSelector::VisitFloat64RoundUp(Node* node) { UNREACHABLE(); }
 
 
+void InstructionSelector::VisitFloat32RoundTruncate(Node* node) {
+  UNREACHABLE();
+}
+
+
 void InstructionSelector::VisitFloat64RoundTruncate(Node* node) {
   X87OperandGenerator g(this);
   Emit(kX87Float64Round | MiscField::encode(kRoundToZero),