Enable snapshots on MIPS. This is based on

src/x64/assembler-x64.h

Index: src/x64/assembler-x64.h
===================================================================
--- src/x64/assembler-x64.h	(revision 11074)
+++ src/x64/assembler-x64.h	(working copy)
@@ -577,8 +577,8 @@
 
   // This sets the branch destination (which is in the instruction on x64).
   // This is for calls and branches within generated code.
-  inline static void set_target_at(Address instruction_payload,
-                                   Address target) {
+  inline static void deserialization_set_special_target_at(
+      Address instruction_payload, Address target) {
     set_target_address_at(instruction_payload, target);
   }
 
@@ -591,8 +591,7 @@
 
   inline Handle<Object> code_target_object_handle_at(Address pc);
   // Number of bytes taken up by the branch target in the code.
-  static const int kCallTargetSize = 4;      // Use 32-bit displacement.
-  static const int kExternalTargetSize = 8;  // Use 64-bit absolute.
+  static const int kSpecialTargetSize = 4;  // Use 32-bit displacement.
   // Distance between the address of the code target in the call instruction
   // and the return address pushed on the stack.
   static const int kCallTargetAddressOffset = 4;  // Use 32-bit displacement.