[snapshot] do not embed string addresses in code.

src/mips64/assembler-mips64.cc

Index: src/mips64/assembler-mips64.cc
diff --git a/src/mips64/assembler-mips64.cc b/src/mips64/assembler-mips64.cc
index 0ad8921ee1fd70f861b86e85291871130925ee42..319e6b8b061f29e41c0b4068c4f64b976b317525 100644
--- a/src/mips64/assembler-mips64.cc
+++ b/src/mips64/assembler-mips64.cc
@@ -2225,7 +2225,11 @@ void Assembler::stop(const char* msg, uint32_t code) {
   // The Simulator will handle the stop instruction and get the message address.
   // On MIPS stop() is just a special kind of break_().
   break_(code, true);
-  emit(reinterpret_cast<uint64_t>(msg));
+  // Do not embed the message string address! We used to do this, but that
+  // made snapshots created from position-independent executable builds
+  // non-deterministic.
+  // TODO(yangguo): remove this field entirely.
+  nop();
 #endif
 }