[x64] Make xmm0 allocatable and use xmm15 as scratch register instead.

src/x64/assembler-x64.h

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 // - Redistributions of source code must retain the above copyright notice,
 // this list of conditions and the following disclaimer.
 //
@@ skipping 168 matching lines @@
   V(xmm10)                  \
   V(xmm11)                  \
   V(xmm12)                  \
   V(xmm13)                  \
   V(xmm14)                  \
   V(xmm15)
 
 #define FLOAT_REGISTERS DOUBLE_REGISTERS
 
 #define ALLOCATABLE_DOUBLE_REGISTERS(V) \
+  V(xmm0)                               \
   V(xmm1)                               \
   V(xmm2)                               \
   V(xmm3)                               \
   V(xmm4)                               \
   V(xmm5)                               \
   V(xmm6)                               \
   V(xmm7)                               \
   V(xmm8)                               \
   V(xmm9)                               \
   V(xmm10)                              \
   V(xmm11)                              \
   V(xmm12)                              \
   V(xmm13)                              \
-  V(xmm14)                              \
-  V(xmm15)
+  V(xmm14)
 
 struct XMMRegister {
   enum Code {
 #define REGISTER_CODE(R) kCode_##R,
     DOUBLE_REGISTERS(REGISTER_CODE)
 #undef REGISTER_CODE
         kAfterLast,
     kCode_no_reg = -1
   };
 
@@ skipping 2066 matching lines @@
   Assembler* assembler_;
 #ifdef DEBUG
   int space_before_;
 #endif
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_X64_ASSEMBLER_X64_H_