Try to fix build of WebAssemblyRegStackify.cpp on Windows

It's failing to build on VS2015 with:

C:\b\build\slave\ClangToTWin\build\src\third_party\llvm\lib\Target\WebAssembly\WebAssemblyRegStackify.cpp(520):
error C2668: 'llvm::make_reverse_iterator': ambiguous call to overloaded function
C:\b\build\slave\ClangToTWin\build\src\third_party\llvm\include\llvm/ADT/STLExtras.h(217):
note: could be 'std::reverse_iterator<llvm::MachineBasicBlock::iterator>
llvm::make_reverse_iterator<llvm::MachineInstrBundleIterator<llvm::MachineInstr>>(IteratorTy)'
        with
        [
            IteratorTy=llvm::MachineInstrBundleIterator<llvm::MachineInstr>
        ]
C:\b\depot_tools\win_toolchain\vs_files\391bbf1220d3edcd3cc3fccdb56224181e3b13a7\win_sdk\bin\..\..\VC\include\xutility(1217):
note: or 'std::reverse_iterator<llvm::MachineBasicBlock::iterator>
std::make_reverse_iterator<llvm::MachineInstrBundleIterator<llvm::MachineInstr>>(_RanIt)' [found using argument-dependent lookup]
        with
        [
            _RanIt=llvm::MachineInstrBundleIterator<llvm::MachineInstr>
        ]

I don't have VS2015 locally at the moment, but hopefully this will help.

llvm-svn: 263418