Enable snapshots on MIPS. This is based on

src/arm/assembler-arm-inl.h

Index: src/arm/assembler-arm-inl.h
===================================================================
--- src/arm/assembler-arm-inl.h	(revision 11074)
+++ src/arm/assembler-arm-inl.h	(working copy)
@@ -80,7 +80,7 @@
 
 
 int RelocInfo::target_address_size() {
-  return Assembler::kExternalTargetSize;
+  return kPointerSize;
 }
 
 
@@ -364,12 +364,18 @@
 }
 
 
-void Assembler::set_target_at(Address constant_pool_entry,
-                              Address target) {
+void Assembler::deserialization_set_special_target_at(
+    Address constant_pool_entry, Address target) {
   Memory::Address_at(constant_pool_entry) = target;
 }
 
 
+void Assembler::set_external_target_at(Address constant_pool_entry,
+                                       Address target) {
+  Memory::Address_at(constant_pool_entry) = target;
+}
+
+
 void Assembler::set_target_address_at(Address pc, Address target) {
   Memory::Address_at(target_address_address_at(pc)) = target;
   // Intuitively, we would think it is necessary to flush the instruction cache