Fix OSX build after changed C++ mangling

[wilzbach]

See #7416 and #7505

Still missing are these:

Undefined symbols for architecture x86_64:
  "symboldata(unsigned long, unsigned int)", referenced from:
      el_ptr(Symbol*) in backend.a(el.o)
      el_convstring(elem*) in backend.a(el.o)
      out_readonly_sym(unsigned int, void*, int) in backend.a(out.o)
      Obj::sym_cdata(unsigned int, char*, int) in backend.a(machobj.o)
  "_align(unsigned long, unsigned long)", referenced from:
      codgen(Symbol*) in backend.a(cgcod.o)
      stackoffsets(int) in backend.a(cgcod.o)
      outjmptab(block*) in backend.a(cod3.o)
      outswitab(block*) in backend.a(cod3.o)
      type_paramsize(TYPE*) in backend.a(type.o)
      alignOffset(int, unsigned long) in backend.a(out.o)
      out_readonly_sym(unsigned int, void*, int) in backend.a(out.o)
      ...
  "ispow2(unsigned long long)", referenced from:
      asmSemantic(AsmStatement*, Scope*) in dmd.o
  "outthunk(Symbol*, Symbol*, unsigned int, unsigned int, unsigned long long, int, unsigned long long)", referenced from:
      toThunkSymbol(FuncDeclaration*, int) in dmd.o
  "Obj::ehtables(Symbol*, unsigned long long, Symbol*)", referenced from:
      except_gentables() in dmd.o

But I'm without OSX, so I first wanted to see whether I'm on the right road here.

[dlang-bot]

Thanks for your pull request, @wilzbach!

Bugzilla references

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[WalterBright]

This is replacing a 64 bit integer with a 32 bit integer. It cannot work correctly.