ppport.h breaks in C++

[FGasper]

    PERL_STATIC_INLINE SV* D_PPP_newSVsv_flags(SV *const old, I32 flags)
        {
            dTHX;
            SV *new = newSV(0);
            sv_setsv_flags(new, old, flags);
            return new;
        }

clang, at least, is choking on SV *new.

[FGasper]

Dupe of #222.