remove unused `FastCall` wrapper

this can just be done using CallWithConv
Upgrade LLVM to close #9117
teach Call/CallWithConv to set attributes
auto merge of #9219 : thestinger/rust/function-split, r=alexcrichton
auto merge of #9118 : alexcrichton/rust/llvm-fix, r=sanxiyn

I created a new branch  rust-llvm-2013-09-11 in my llvm repo to mark this momentous occasion