Fix profiler performance test
Fix profiler performance test

We used to use a volatile store, but recently LLVM started stripping volatile stores that are clobbered by a later store. atomic stores suffer the same fate. Using empty asm volatile blocks around the store seems to prevent the code motion and dead store elimination without hurting runtime.
psuriana/Halide,delcypher/Halide,dan-tull/Halide,ronen/Halide,myrtleTree33/Halide,dan-tull/Halide,mcanthony/Halide,psuriana/Halide,ronen/Halide,fengzhyuan/Halide,mcanthony/Halide,dan-tull/Halide,jiawen/Halide,ronen/Halide,fengzhyuan/Halide,adasworks/Halide,fengzhyuan/Halide,adasworks/Halide,tdenniston/Halide,jiawen/Halide,delcypher/Halide,kgnk/Halide,dougkwan/Halide,adasworks/Halide,psuriana/Halide,adasworks/Halide,fengzhyuan/Halide,kgnk/Halide,myrtleTree33/Halide,kenkuang1213/Halide,tdenniston/Halide,smxlong/Halide,kenkuang1213/Halide,dougkwan/Halide,fengzhyuan/Halide,psuriana/Halide,adasworks/Halide,ronen/Halide,psuriana/Halide,mcanthony/Halide,kenkuang1213/Halide,fengzhyuan/Halide,smxlong/Halide,tdenniston/Halide,ronen/Halide,jiawen/Halide,jiawen/Halide,psuriana/Halide,smxlong/Halide,kenkuang1213/Halide,smxlong/Halide,myrtleTree33/Halide,dan-tull/Halide,ronen/Halide,adasworks/Halide,kgnk/Halide,kenkuang1213/Halide,dougkwan/Halide,smxlong/Halide,tdenniston/Halide,mcanthony/Halide,delcypher/Halide,dan-tull/Halide,delcypher/Halide,jiawen/Halide,kgnk/Halide,tdenniston/Halide,dougkwan/Halide,jiawen/Halide,smxlong/Halide,tdenniston/Halide,dougkwan/Halide,mcanthony/Halide,mcanthony/Halide,kgnk/Halide,mcanthony/Halide,tdenniston/Halide,adasworks/Halide,dougkwan/Halide,kenkuang1213/Halide,dougkwan/Halide,myrtleTree33/Halide,delcypher/Halide,psuriana/Halide,myrtleTree33/Halide,kenkuang1213/Halide,fengzhyuan/Halide,delcypher/Halide,ronen/Halide,delcypher/Halide,tdenniston/Halide,smxlong/Halide,delcypher/Halide,dan-tull/Halide,smxlong/Halide,kgnk/Halide,jiawen/Halide,adasworks/Halide,ronen/Halide,dan-tull/Halide,kgnk/Halide,kgnk/Halide,myrtleTree33/Halide,kenkuang1213/Halide,myrtleTree33/Halide,dougkwan/Halide,fengzhyuan/Halide,myrtleTree33/Halide,dan-tull/Halide,mcanthony/Halide