X87: add part of backend support for X87.

port r24179.  we add the corresponding function implementation to pass
   the compilation.

original commit message:

   [turbofan] Add backend support for float32.

BUG=
R=weiliang.lin@intel.com

Review URL: https://codereview.chromium.org/602003002

Patch from Chunyang Dai <chunyang.dai@intel.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24196 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/x87/assembler-x87.h

@@ -148,6 +148,13 @@ struct X87Register {
     return kMaxNumAllocatableRegisters;
   }
 
+
+  // TODO(turbofan): Proper support for float32.
+  static int NumAllocatableAliasedRegisters() {
+    return NumAllocatableRegisters();
+  }
+
+
   static int ToAllocationIndex(X87Register reg) {
     return reg.code_;
   }