[MS ABI] Implement thread-safe initialization using the MSVC 2015 ABI

The MSVC 2015 ABI utilizes a rather straightforward adaptation of the
algorithm found in the appendix of N2382.  While we are here, implement
support for emitting cleanups if an exception is thrown while we are
intitializing a static local variable.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@236697 91177308-0d34-0410-b5e6-96231b3b80d8