Subzero: Add sandboxing for x86-32.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4079
R=jvoung@chromium.org, kschimpf@google.com

Review URL: https://codereview.chromium.org/930733002
diff --git a/src/assembler.cpp b/src/assembler.cpp
index b0ff419..d131426 100644
--- a/src/assembler.cpp
+++ b/src/assembler.cpp
@@ -40,7 +40,8 @@
   F->set_position(0);
   F->set_kind(Kind);
   F->set_value(Value);
-  fixups_.push_back(F);
+  if (!assembler_.getPreliminary())
+    fixups_.push_back(F);
   return F;
 }