rustc_trans: 'assume' intrinsic is only available on LLVM >= 3.6
rustc_trans: 'assume' intrinsic is only available on LLVM >= 3.6

Based on the patch from Luca Bruno.

Instead of creating an empty C function in the rt, this version creates an shim
noop function using llvm. This function is declared as internal, and the
unsupported assume intrinsic and the shim gets completly removed by the
optimizer.

dwillmer/rust,jashank/rust,zubron/rust,l0kod/rust,aepsil0n/rust,mvdnes/rust,aepsil0n/rust,mvdnes/rust,nwin/rust,jashank/rust,KokaKiwi/rust,TheNeikos/rust,dwillmer/rust,vhbit/rust,zachwick/rust,zachwick/rust,aidancully/rust,mvdnes/rust,jroesch/rust,aneeshusa/rust,l0kod/rust,robertg/rust,omasanori/rust,TheNeikos/rust,pelmers/rust,vhbit/rust,GBGamer/rust,mvdnes/rust,GBGamer/rust,aepsil0n/rust,dwillmer/rust,omasanori/rust,aidancully/rust,vhbit/rust,omasanori/rust,l0kod/rust,jashank/rust,aneeshusa/rust,GBGamer/rust,pelmers/rust,dwillmer/rust,l0kod/rust,mihneadb/rust,graydon/rust,reem/rust,pshc/rust,jroesch/rust,TheNeikos/rust,TheNeikos/rust,graydon/rust,aneeshusa/rust,vhbit/rust,jroesch/rust,zachwick/rust,nwin/rust,graydon/rust,zachwick/rust,reem/rust,reem/rust,KokaKiwi/rust,dwillmer/rust,robertg/rust,reem/rust,mihneadb/rust,pshc/rust,pshc/rust,dwillmer/rust,omasanori/rust,pelmers/rust,pshc/rust,aidancully/rust,graydon/rust,robertg/rust,pelmers/rust,jroesch/rust,KokaKiwi/rust,robertg/rust,zubron/rust,mihneadb/rust,mihneadb/rust,jashank/rust,GBGamer/rust,nwin/rust,mvdnes/rust,nwin/rust,zachwick/rust,zachwick/rust,mihneadb/rust,aepsil0n/rust,aneeshusa/rust,nwin/rust,aidancully/rust,l0kod/rust,vhbit/rust,zubron/rust,zubron/rust,reem/rust,jashank/rust,pshc/rust,jashank/rust,vhbit/rust,pshc/rust,pelmers/rust,robertg/rust,dwillmer/rust,reem/rust,zubron/rust,omasanori/rust,l0kod/rust,graydon/rust,graydon/rust,GBGamer/rust,nwin/rust,jroesch/rust,aidancully/rust,l0kod/rust,KokaKiwi/rust,jashank/rust,robertg/rust,GBGamer/rust,mihneadb/rust,l0kod/rust,nwin/rust,aidancully/rust,TheNeikos/rust,mvdnes/rust,aneeshusa/rust,jroesch/rust,TheNeikos/rust,omasanori/rust,zubron/rust,aneeshusa/rust,nwin/rust,vhbit/rust,jroesch/rust,pshc/rust,jashank/rust,pshc/rust,KokaKiwi/rust,zubron/rust,GBGamer/rust,vhbit/rust,pelmers/rust,jroesch/rust,KokaKiwi/rust,aepsil0n/rust,GBGamer/rust,zubron/rust,dwillmer/rust,aepsil0n/rust