Fix compiler error encountered by Flutter

runtime/vm/compiler.cc

Index: runtime/vm/compiler.cc
diff --git a/runtime/vm/compiler.cc b/runtime/vm/compiler.cc
index d5ceba554976cfda899536d8aff672df60e173dc..59a3d0e2ca84098cb91f12aa20c089032b73f422 100644
--- a/runtime/vm/compiler.cc
+++ b/runtime/vm/compiler.cc
@@ -574,7 +574,7 @@ bool CompileParsedFunctionHelper::Compile(CompilationPipeline* pipeline) {
   // 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;