Fix compiler error encountered by Flutter

runtime/vm/compiler.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/compiler.h"
 
 #include "vm/assembler.h"
 
 #include "vm/ast_printer.h"
 #include "vm/block_scheduler.h"
@@ skipping 556 matching lines @@
 #endif
   CSTAT_TIMER_SCOPE(thread(), codegen_timer);
   HANDLESCOPE(thread());
 
   // We may reattempt compilation if the function needs to be assembled using
   // far branches on ARM and MIPS. In the else branch of the setjmp call,
   // done is set to false, and use_far_branches is set to true if there is a
   // longjmp from the ARM or MIPS assemblers. In all other paths through this
   // while loop, done is set to true. use_far_branches is always false on ia32
   // and x64.
-  bool done = false;
+  volatile bool done = false;
   // volatile because the variable may be clobbered by a longjmp.
   volatile bool use_far_branches = false;
   const bool use_speculative_inlining = false;
 
   while (!done) {
     const intptr_t prev_deopt_id = thread()->deopt_id();
     thread()->set_deopt_id(0);
     LongJumpScope jump;
     const intptr_t val = setjmp(*jump.Set());
     if (val == 0) {
@@ skipping 1294 matching lines @@
 }
 
 
 void BackgroundCompiler::EnsureInit(Thread* thread) {
   UNREACHABLE();
 }
 
 #endif  // DART_PRECOMPILED_RUNTIME
 
 }  // namespace dart