Fix JIT initialization race

See b/8767735 Slow thread in thread spin test

A race exists in thread creation/JIT initialization that can
leave the JIT permanantly disabled for a thread (typically
the first interpreter thread).

(cherry-pick of 67985d960f5c877f86d0bba251d2d55c7a062b8d.)

Change-Id: Ic7e3a1cde2833ac78455fa5d465156b5e0896fc1