Revert "Revert "Revert 220932.": "Removing the static initializer in...

Revert "Revert "Revert 220932.": "Removing the static initializer in ManagedStatic.cpp by using llvm_call_once to initialize the ManagedStatic mutex""

This reverts commit r269577.
Broke NetBSD, waiting for Kamil to investigate

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 269584