Lazy JIT thread safety

http://llvm.org/PR5184 describes two problems with thread-safety in
the lazy JIT compiler, the first of which is quite hard to fix if we
can fix it at all. Could the people who currently use the lazy
compiler speak up either here or on the bug and say what they think
the path forward should be? I'm not volunteering to implement the
whole thing, but I keep having to modify the JIT, and knowing the
eventual goal would let me make incremental progress toward it.

Thanks,
Jeffrey