Updating documentation as per Chandler's feedback.

Updating documentation as per Chandler's feedback.

This goes with the earlier commit to remove the static destructor from ManagedStatic.cpp by controlling the allocation and de-allocation of the mutex.

Summary: This is part of the ongoing work to remove static constructors and destructors.

Reviewers: chandlerc, rnk

Reviewed By: rnk

Subscribers: rnk, llvm-commits

Differential Revision: http://reviews.llvm.org/D5473

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219640 91177308-0d34-0410-b5e6-96231b3b80d8