[turbofan] Add backend support for float32.

src/ia32/assembler-ia32.h

Index: src/ia32/assembler-ia32.h
diff --git a/src/ia32/assembler-ia32.h b/src/ia32/assembler-ia32.h
index 81757788f0931421eed718e0dd4ab256bb9d3d52..8d4a81901c1da08b4ed7341d914ac9a787f91ff1 100644
--- a/src/ia32/assembler-ia32.h
+++ b/src/ia32/assembler-ia32.h
@@ -148,6 +148,11 @@ struct XMMRegister {
     return kMaxNumAllocatableRegisters;
   }
 
+  // TODO(turbofan): Proper support for float32.
+  static int NumAllocatableRegistersForTurbofan() {
+    return NumAllocatableRegisters();
+  }
+
   static int ToAllocationIndex(XMMRegister reg) {
     DCHECK(reg.code() != 0);
     return reg.code() - 1;