PPC: [turbofan] Implemented the optional Float32RoundTruncate operator.

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

Index: src/compiler/ppc/instruction-selector-ppc.cc
diff --git a/src/compiler/ppc/instruction-selector-ppc.cc b/src/compiler/ppc/instruction-selector-ppc.cc
index 2934f238937798e5af0ae638ed39b010893aac5e..68cc6bf9fa63addaa8e26878e109ca29d4590cb3 100644
--- a/src/compiler/ppc/instruction-selector-ppc.cc
+++ b/src/compiler/ppc/instruction-selector-ppc.cc
@@ -1159,7 +1159,7 @@ void InstructionSelector::VisitFloat64RoundUp(Node* node) {
 
 
 void InstructionSelector::VisitFloat32RoundTruncate(Node* node) {
-  UNREACHABLE();
+  VisitRR(this, kPPC_TruncateDouble, node);
 }
 
 
@@ -1691,6 +1691,7 @@ InstructionSelector::SupportedMachineOperatorFlags() {
          MachineOperatorBuilder::kFloat64RoundDown |
          MachineOperatorBuilder::kFloat32RoundUp |
          MachineOperatorBuilder::kFloat64RoundUp |
+         MachineOperatorBuilder::kFloat32RoundTruncate |
          MachineOperatorBuilder::kFloat64RoundTruncate |
          MachineOperatorBuilder::kFloat64RoundTiesAway |
          MachineOperatorBuilder::kWord32Popcnt |