Fix bugs in simplified lowering relating to int32/uint32 signs.

test/cctest/compiler/test-js-context-specialization.cc

Index: test/cctest/compiler/test-js-context-specialization.cc
diff --git a/test/cctest/compiler/test-js-context-specialization.cc b/test/cctest/compiler/test-js-context-specialization.cc
index 264fee085390dfcad241604eed69e18839268e41..f04e3279d320a97581fcfbf8ca740058c8ae78cb 100644
--- a/test/cctest/compiler/test-js-context-specialization.cc
+++ b/test/cctest/compiler/test-js-context-specialization.cc
@@ -21,7 +21,7 @@ class ContextSpecializationTester : public HandleAndZoneScope,
       : DirectGraphBuilder(new (main_zone()) Graph(main_zone())),
         common_(main_zone()),
         javascript_(main_zone()),
-        machine_(),
+        machine_(main_zone()),
         simplified_(main_zone()),
         jsgraph_(graph(), common(), &javascript_, &machine_),
         info_(main_isolate(), main_zone()) {}