[turbofan] Implemented the optional Float32RoundTruncate operator.

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

Index: src/compiler/mips/instruction-selector-mips.cc
diff --git a/src/compiler/mips/instruction-selector-mips.cc b/src/compiler/mips/instruction-selector-mips.cc
index 7c13a2c012eb729967b1965a150de4e861c1d81d..b6785e32976c95034bf65e64d63b35366253cdef 100644
--- a/src/compiler/mips/instruction-selector-mips.cc
+++ b/src/compiler/mips/instruction-selector-mips.cc
@@ -663,6 +663,11 @@ void InstructionSelector::VisitFloat64RoundUp(Node* node) {
 }
 
 
+void InstructionSelector::VisitFloat32RoundTruncate(Node* node) {
+  UNREACHABLE();
+}
+
+
 void InstructionSelector::VisitFloat64RoundTruncate(Node* node) {
   VisitRR(this, kMipsFloat64RoundTruncate, node);
 }