[PATCH] [ms-cxxabi] Implement guard variables for static initialization

[Reid Kleckner]

Hi rjmccall,

Static locals requiring initialization are not thread safe on Windows.
Unfortunately, it's possible to create static locals that are actually
externally visible with inline functions and templates.  As a result, we
have to implement an initialization guard scheme that is compatible with
TUs built by MSVC, which makes thread safety prohibitively difficult.

MSVC's scheme is that every function that requires a guard gets an i32
bitfield.  Each static local is assigned a bit that indicates if it has
been initialized, up to 32 bits, at which point a new bitfield is
created.  MSVC rejects inline functions with more than 32 static locals,
and the externally visible mangling (?_B) only allows for one guard
variable per function.

Implements PR16888.

http://llvm-reviews.chandlerc.com/D1416

Files:
  include/clang/AST/Mangle.h
  lib/AST/ItaniumMangle.cpp
  lib/AST/MicrosoftMangle.cpp
  lib/CodeGen/CGCXXABI.cpp
  lib/CodeGen/CGCXXABI.h
  lib/CodeGen/CGDeclCXX.cpp
  lib/CodeGen/CodeGenFunction.cpp
  lib/CodeGen/CodeGenFunction.h
  lib/CodeGen/ItaniumCXXABI.cpp
  lib/CodeGen/MicrosoftCXXABI.cpp
  test/CodeGenCXX/microsoft-abi-static-initializers.cpp
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