Fix warnings and error building swift/SILOptimizer on Windows with MSVC

[hughbe]

• Control path uncovered warning
• Non accessible method error
• Can't friend class error
• Sign conversion warnings
• Internal stdlib assertitions when compiling swift code

[rudkx]

Otherwise LGTM but @eeckstein should probably take a quick look.

[rudkx]

The indentation is off here.

[hughbe]

Thanks, I also removed the double new line

[jrose-apple]

I think the right way to fix this is just friend SCCVisitor;, not to make the visit method public.

[hughbe]

I get an error: “class template has already been declared as a non-class template”

I think the fix is to change this to friend class SCCVisitor<IVInfo> which compiles in VS. I'm running a full build now to make sure.

EDIT: friend SCCVisitor also works, so I went for your suggestion instead

[jrose-apple]

SetVector has a getArrayRef method you can use instead.

[hughbe]

good idea, I also removed the MSVC comment

[jrose-apple]

Please wrap to 80 columns.

[hughbe]

fixed

[eeckstein]

LGTM

[jrose-apple]

@swift-ci Please smoke test and merge

[hughbe]

This didn't get merged either although tests passed!