MFC debug info for variadic functions

r264826: Merge LLVM r202188:

    Debug info: Support variadic functions.
    Variadic functions have an unspecified parameter tag after the last
    argument. In IR this is represented as an unspecified parameter in the
    subroutine type.

    Paired commit with CFE r202185.

    rdar://problem/13690847

    This re-applies r202184 + a bugfix in DwarfDebug's argument handling.

  This merge includes a change to use the LLVM 3.4 API in
  lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp:

  DwarfUnit -> CompileUnit

r264827: Merge Clang r202185:

    Debug info: Generate debug info for variadic functions.
    Paired commit with LLVM.

    rdar://problem/13690847

  This merege includes changes to use the Clang 3.4 API (revisions
  199686 and 200082) in lib/CodeGen/CGDebugInfo.cpp:

  getParamType  -> getArgType
  getNumParams  -> getNumArgs
  getReturnType -> getResultType

r264828: Add patches corresponding to r264826 and r264827

Sponsored by:	DARPA, AFRL