Fix compiler errors that seem to show up in the Android build under mojo/sky

Fix compiler errors that seem to show up in the Android build under mojo/sky

../../dart/runtime/vm/compiler.cc: In static member function 'static dart::RawError* dart::Compiler::Compile(const dart::Library&, const dart::Script&)':
../../dart/runtime/vm/compiler.cc:181:18: error: variable 'isolate' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
   Isolate* const isolate = Isolate::Current();
                  ^
../../dart/runtime/vm/compiler.cc: In static member function 'static dart::RawObject* dart::Compiler::EvaluateStaticInitializer(const dart::Field&)':
../../dart/runtime/vm/compiler.cc:1145:18: error: variable 'isolate' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
   Isolate* const isolate = Isolate::Current();
                  ^

Committed: https://code.google.com/p/dart/source/detail?r=44850

[siva, 2015-04-01 21:35:32]

asiva@google.com changed reviewers:
+ koda@google.com

[siva, 2015-04-01 23:11:00]

Committed patchset #3 (id:40001) manually as r44850 (presubmit successful).