Reland: [turbofan] Various fixes to allow unboxed doubles as arguments in registers and on the stac…

test/cctest/compiler/c-signature.h

Index: test/cctest/compiler/c-signature.h
diff --git a/test/cctest/compiler/c-signature.h b/test/cctest/compiler/c-signature.h
index 83b3328a3b4e256274f7a2c898fee26d42825dd7..8eaf6325f22011081d6a6a957440c66aae44248d 100644
--- a/test/cctest/compiler/c-signature.h
+++ b/test/cctest/compiler/c-signature.h
@@ -69,6 +69,10 @@ class CSignature : public MachineSignature {
     }
   }
 
+  static CSignature* FromMachine(Zone* zone, MachineSignature* msig) {
+    return reinterpret_cast<CSignature*>(msig);
+  }
+
   static CSignature* New(Zone* zone, MachineType ret,
                          MachineType p1 = kMachNone, MachineType p2 = kMachNone,
                          MachineType p3 = kMachNone, MachineType p4 = kMachNone,