x64: Fix safepoint register index calculation.

src/x64/assembler-x64.h

Index: src/x64/assembler-x64.h
diff --git a/src/x64/assembler-x64.h b/src/x64/assembler-x64.h
index 6e1837d7e2150d23560d6a8c3c24e06bfd73a8f7..0bcb776341498c96ec33f17f794713441066abaf 100644
--- a/src/x64/assembler-x64.h
+++ b/src/x64/assembler-x64.h
@@ -109,7 +109,9 @@ struct Register {
   }
 
   static int ToRspIndexForPushAll(Register reg) {
-    return kRspIndexForPushAllByRegisterCode[reg.code()];
+    // TODO(ager): Refactor this so we can use the right constants for
+    // this computation. Move it to the macro assembler as on ARM.
+    return kRspIndexForPushAllByRegisterCode[reg.code()] + 5;
   }
 
   static const char* AllocationIndexToString(int index) {