added support for release branches of clang and llvm via git. fixes #3

fixes issue #3 that I created earlier.
Added clang 3.4 - mingw64 needs 3.4 so that's why I'm doing this early ;)
Seems to not break anything and just git pull's to update as we get closer and closer to 3.4 tag which is due 23rd December

We can then change it to CT_GetFile after llvm site add's it

Also head should clone faster because I'm using --single-branch

All those precious seconds / harddrive space matter :D

Martell