Add x64 implementation test support for assembler and code generator.

src/bootstrapper.cc

Index: src/bootstrapper.cc
===================================================================
--- src/bootstrapper.cc	(revision 2140)
+++ src/bootstrapper.cc	(working copy)
@@ -1113,6 +1113,9 @@
   }
 
 #ifdef V8_HOST_ARCH_64_BIT
+  // TODO(X64): Remove these tests when code generation works and is stable.
+  MacroAssembler::ConstructAndTestJSFunction();
+  CodeGenerator::TestCodeGenerator();
   // TODO(X64): Reenable remaining initialization when code generation works.
   return true;
 #endif  // V8_HOST_ARCH_64_BIT