Fix compilation failure when v8 compiled with GCC 5.x due to `-Werror=unused-variable`

BUG=

Review-Url: https://codereview.chromium.org/2212133003
Cr-Commit-Position: refs/heads/master@{#38385}

test/unittests/compiler/linkage-tail-call-unittest.cc

@@ -26,6 +26,7 @@ class LinkageTailCall : public TestWithZone {
   CallDescriptor* NewStandardCallDescriptor(LocationSignature* locations) {
     DCHECK(arraysize(kMachineTypes) >=
            locations->return_count() + locations->parameter_count());
+    USE(kMachineTypes);
     return new (zone()) CallDescriptor(
         CallDescriptor::kCallCodeObject, MachineType::AnyTagged(),
         LinkageLocation::ForAnyRegister(MachineType::Pointer()),