Allow non-native ARM builds
Allow non-native ARM builds

CodeGen.cpp wasn't calling InitializeXXXAsmParser() for any target,
which meant that (e.g.) generating ARM on an x86 host would fail. Code
was restructured a bit to only init AsmParser/AsmPrinter for targets
that actually have them (e.g., NVPTX doesn't have AsmParser).

kgnk/Halide,adasworks/Halide,myrtleTree33/Halide,dan-tull/Halide,rodrigob/Halide,smxlong/Halide,dougkwan/Halide,gchauras/Halide,aam/Halide,dougkwan/Halide,kenkuang1213/Halide,tdenniston/Halide,mcanthony/Halide,rodrigob/Halide,fengzhyuan/Halide,ronen/Halide,lglucin/Halide,ronen/Halide,adasworks/Halide,dougkwan/Halide,smxlong/Halide,dan-tull/Halide,jiawen/Halide,aam/Halide,ronen/Halide,ayanazmat/Halide,psuriana/Halide,kgnk/Halide,dougkwan/Halide,delcypher/Halide,smxlong/Halide,smxlong/Halide,dan-tull/Halide,myrtleTree33/Halide,tdenniston/Halide,lglucin/Halide,kenkuang1213/Halide,dan-tull/Halide,myrtleTree33/Halide,delcypher/Halide,kenkuang1213/Halide,fengzhyuan/Halide,jiawen/Halide,rodrigob/Halide,lglucin/Halide,myrtleTree33/Halide,mcanthony/Halide,mcanthony/Halide,ayanazmat/Halide,mcanthony/Halide,jiawen/Halide,rodrigob/Halide,aam/Halide,kgnk/Halide,kgnk/Halide,adasworks/Halide,delcypher/Halide,fengzhyuan/Halide,aam/Halide,rodrigob/Halide,aam/Halide,tdenniston/Halide,adasworks/Halide,myrtleTree33/Halide,tdenniston/Halide,kenkuang1213/Halide,jiawen/Halide,dan-tull/Halide,mikeseven/Halide,adasworks/Halide,damienfir/Halide,smxlong/Halide,damienfir/Halide,ayanazmat/Halide,lglucin/Halide,damienfir/Halide,psuriana/Halide,tdenniston/Halide,adasworks/Halide,fengzhyuan/Halide,gchauras/Halide,tdenniston/Halide,kenkuang1213/Halide,fengzhyuan/Halide,mcanthony/Halide,fengzhyuan/Halide,smxlong/Halide,adasworks/Halide,psuriana/Halide,mikeseven/Halide,smxlong/Halide,kgnk/Halide,jiawen/Halide,rodrigob/Halide,kgnk/Halide,smxlong/Halide,rodrigob/Halide,myrtleTree33/Halide,aam/Halide,damienfir/Halide,delcypher/Halide,kgnk/Halide,myrtleTree33/Halide,mikeseven/Halide,fengzhyuan/Halide,jiawen/Halide,ronen/Halide,dougkwan/Halide,ronen/Halide,dan-tull/Halide,ayanazmat/Halide,delcypher/Halide,delcypher/Halide,damienfir/Halide,jiawen/Halide,dougkwan/Halide,ronen/Halide,myrtleTree33/Halide,dougkwan/Halide,lglucin/Halide,mikeseven/Halide,psuriana/Halide,gchauras/Halide,fengzhyuan/Halide,ayanazmat/Halide,damienfir/Halide,ayanazmat/Halide,ayanazmat/Halide,adasworks/Halide,psuriana/Halide,kgnk/Halide,tdenniston/Halide,damienfir/Halide,mcanthony/Halide,lglucin/Halide,aam/Halide,ronen/Halide,delcypher/Halide,kenkuang1213/Halide,kenkuang1213/Halide,gchauras/Halide,mcanthony/Halide,kenkuang1213/Halide,dan-tull/Halide,delcypher/Halide,ronen/Halide,rodrigob/Halide,gchauras/Halide,gchauras/Halide,mikeseven/Halide,mcanthony/Halide,tdenniston/Halide,psuriana/Halide,dougkwan/Halide,lglucin/Halide,damienfir/Halide,psuriana/Halide,ayanazmat/Halide,dan-tull/Halide