Make experimental/gc compilable on Mac OS.

src/isolate.cc

Index: src/isolate.cc
===================================================================
--- src/isolate.cc	(revision 8847)
+++ src/isolate.cc	(working copy)
@@ -1700,12 +1700,6 @@
   CpuProfiler::Setup();
   HeapProfiler::Setup();
 
-  // If the serializer is enabled we will use only the platform to determine
-  // the CPU.  We can do that without generating probe code, so we don't need
-  // the heap to be set up first.  We move up the detection to here so that
-  // the builtins can make use of the information.
-  if (Serializer::enabled()) CPU::Setup();
-
   // Initialize other runtime facilities
 #if defined(USE_SIMULATOR)
 #if defined(V8_TARGET_ARCH_ARM) || defined(V8_TARGET_ARCH_MIPS)