[turbofan] Tester improvements; use CSignature and simplify ReturnValueTraits.

test/cctest/compiler/test-run-machops.cc

Index: test/cctest/compiler/test-run-machops.cc
diff --git a/test/cctest/compiler/test-run-machops.cc b/test/cctest/compiler/test-run-machops.cc
index 66ac809a5c22cb236600f83b1654bd6d7f1a6024..036c1fb5bca7af53b125ed564b2b032d02d9ab59 100644
--- a/test/cctest/compiler/test-run-machops.cc
+++ b/test/cctest/compiler/test-run-machops.cc
@@ -4412,7 +4412,7 @@ TEST(RunTestIntPtrArithmetic) {
 
 TEST(RunSpillLotsOfThings) {
   static const int kInputSize = 1000;
-  RawMachineAssemblerTester<void> m;
+  RawMachineAssemblerTester<int32_t> m;
   Node* accs[kInputSize];
   int32_t outputs[kInputSize];
   Node* one = m.Int32Constant(1);