[PATCH] Removing the static initializer in ManagedStatic.cpp by using llvm_call_once to initialize the ManagedStatic mutex.

[Chris Bieneman]

I can re-work this to be an alias of call_once when available. I think in the absence of call_once the hand rolled solution should be sufficient. I'm curious what David thinks the issues with the hand rolled implementation are. I'm pretty good WRT lock-free multi-threading, and I don't spot anything. Also, since we're using pretty much that same code in pass initialization, if there are issues we should identify and solve them.

http://reviews.llvm.org/D5922