Widen integer literal to unsigned when required

[serenity4]

Fixes #515.

This include an additional fix with txt_no_sfx = replace(txt_no_sfx, r"^0X" => "0x") to also support integer constants formatted as 0X012345678, which otherwise throw an error when executed.

[JamesWrigley]

Would be nice to make a changelog entry too :)

[serenity4]

Nightly failures seem unrelated, locally the fix handles hexadecimal and decimal literal integers correctly (using Clong by default and only wrap in Culong when the value doesn't fit).

[JamesWrigley]

Sorry forgot to mention, could we add a test too? I would recommend adding a header file in https://github.com/JuliaInterop/Clang.jl/tree/master/test/include and then using it in https://github.com/JuliaInterop/Clang.jl/blob/master/test/generators.jl.

[serenity4]

Sure, thanks for the pointer! Should be good now. There is a test failure on x64, looking at it now.

[serenity4]

All good :)

[JamesWrigley]

Unofficial LGTM!

[Gnimuc]

Thanks！