Remove broken _WIN64 checks.

src/compiler/x64/instruction-selector-x64.cc

Index: src/compiler/x64/instruction-selector-x64.cc
diff --git a/src/compiler/x64/instruction-selector-x64.cc b/src/compiler/x64/instruction-selector-x64.cc
index bd2969e0cf4c796e891041fc7f5289eb553273cf..f97fc3881e0f301cf8e9effc12e75f1e069912b0 100644
--- a/src/compiler/x64/instruction-selector-x64.cc
+++ b/src/compiler/x64/instruction-selector-x64.cc
@@ -9,8 +9,6 @@ namespace v8 {
 namespace internal {
 namespace compiler {
 
-#ifndef _WIN64
-
 // Adds X64-specific methods for generating operands.
 class X64OperandGenerator V8_FINAL : public OperandGenerator {
  public:
@@ -719,8 +717,6 @@ void InstructionSelector::VisitCall(Node* call, BasicBlock* continuation,
   }
 }
 
-#endif
-
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8