CmmToLlvm: Sign/Zero extend parameters for foreign calls

This is basically a backport of 0ac5860e. However, due to some differences between mainline and 8.10 I had to adjust a couple of things. For example, compiler/GHC/Platform.hs doesn't exist and therefore there exists no straight forward place for platformCConvNeedsExtension. Thus I added it to the only call side. In order to not deviate from mainline to much I added ppVar' and ppTypeLit' to the pretty printers. Instead I could also just duplicate and inline them to the single call side. Any thoughts about this?