Based loosely on the the previous patch attempts.
Patch alters many files to insert export definitions that VC++ can use during library generation.
Added a dirent.h (originally from http://www.softagalleria.net/dirent.php\) to the Win32 directory. This file is under the GPL-compatable MIT License.
Added Makefile.vc to the Win32 directory. This file is an NMake makefile, and should operate correctly under x86 and x64, for any version of VC 6 - 10.
Use from a VC command prompt: nmake -f win32\Makefile.vc
The only caveat is that a define will need to be added to the non-windows build files to define CPP_EXPORT=[blank]. I wasn't sure the proper location in the existing setup to inject that, so I'm leaving it to someone more experienced with aspell dev than myself.
Corrected diff
This issue has moved to GitHub: https://github.com/GNUAspell/aspell/issues/502