Decouple CpuFeatures from serializer state.

src/platform.h

Index: src/platform.h
diff --git a/src/platform.h b/src/platform.h
index e2e4cb96789b42a17c4c0d04408fe41a69468d28..65e8cc5b04622868c292b907c0d1353fb9ce4148 100644
--- a/src/platform.h
+++ b/src/platform.h
@@ -272,7 +272,7 @@ class OS {
   // This is a little messy because the interpretation is subject to the cross
   // of the CPU and the OS.  The bits in the answer correspond to the bit
   // positions indicated by the members of the CpuFeature enum from globals.h
-  static uint64_t CpuFeaturesImpliedByPlatform();
+  static unsigned CpuFeaturesImpliedByPlatform();
 
   // The total amount of physical memory available on the current system.
   static uint64_t TotalPhysicalMemory();