[noupstream] Instrument for thread suspension.

When given command line flag -finstrument-for-thread-suspension, generate instrumentation calls for function entry and back edges.

Instrumentation call now looks like:
  __nacl_suspend_thread_if_needed ();

BUG=http://code.google.com/p/nativeclient/issues/detail?id=826
TEST=

Review URL: http://codereview.chromium.org/3320011