[D-runtime] druntime fixes again break Windows DLL support

[Rainer Schuetze]

Walter Bright wrote:
> ..\dmd mydll.obj ..\druntime\lib\gcstub.obj mydll.def -L/map
> OPTLINK (R) for Win32  Release 8.00.12
> Copyright (C) Digital Mars 1989-2010  All rights reserved.
> http://www.digitalmars.com/ctg/optlink.html
> mydll.obj(mydll)
>  Error 42: Symbol Undefined 
> _D4core10dll_helper18dll_process_attachFT4core3sys7windows7windows6HANDL
> EbZb
> mydll.obj(mydll)
>  Error 42: Symbol Undefined 
> _D4core10dll_helper18dll_process_detachFT4core3sys7windows7windows6HANDL
> EbZv
> mydll.obj(mydll)
>  Error 42: Symbol Undefined _D4core10dll_helper12__ModuleInfoZ
> --- errorlevel 3

copying from the D newsgroup: core/dll_helper.d has been recently moved 
to core/sys/windows/_dll.d, so you might just have the old import file 
core/dll_helper.di lying around on your disk and referenced without the 
correspondent file being built into druntime.