Add the target platform to the .dub/build/* cache folders.
Add the target platform to the .dub/build/* cache folders.

Enables sharing of the same package folders for different platforms.

Flamaros/dub,y12uc231/dub,grogancolin/dub,schuetzm/dub,alexeibs/dub,jelmansouri/dub,D-Programming-Language/dub,rjframe/dub,Abscissa/dub,Geod24/dub,gedaiu/dub,Abscissa/dub-data-mod,xentec/dub,dreamsxin/dub,jeanbaptistelab/dub,nazriel/dub,p0nce/dub