`simple_variant_dir` example does not build on Windows

[mwichmann]

It's too naiive about the games you have to play

lib /nologo /OUT:build\chocolate\liba\a.lib build\chocolate\liba\lib.obj
link /nologo /OUT:build\chocolate\app\app.exe /LIBPATH:build\chocolate\liba a.lib build\chocolate\app\app.obj
app.obj : error LNK2019: unresolved external symbol __imp_add referenced in function main
build\chocolate\app\app.exe : fatal error LNK1120: 1 unresolved externals
scons: *** [build\chocolate\app\app.exe] Error 1120

Works fine on Linux/gcc.