[pre-commit-benchmark] Default to one run at -O3
[pre-commit-benchmark] Default to one run at -O3

Also add a -O option that allows one to specify desired optimization
levels.  This will make it much easier to get a lightweight answer to
"did I speed things up?" while still allowing

  pre-commit-benchmark -r3 -O3 -Ofast -O0

to do a more thorough test.

Swift SVN r19741

brentdax/swift,manavgabhawala/swift,huonw/swift,khizkhiz/swift,kstaring/swift,ben-ng/swift,airspeedswift/swift,rudkx/swift,kperryua/swift,shajrawi/swift,austinzheng/swift,manavgabhawala/swift,amraboelela/swift,practicalswift/swift,swiftix/swift,aschwaighofer/swift,xedin/swift,manavgabhawala/swift,tjw/swift,felix91gr/swift,apple/swift,swiftix/swift.old,xedin/swift,gottesmm/swift,karwa/swift,felix91gr/swift,atrick/swift,sschiau/swift,emilstahl/swift,gribozavr/swift,emilstahl/swift,stephentyrone/swift,jmgc/swift,slavapestov/swift,alblue/swift,devincoughlin/swift,huonw/swift,djwbrown/swift,practicalswift/swift,khizkhiz/swift,practicalswift/swift,jopamer/swift,kperryua/swift,Ivacker/swift,KrishMunot/swift,brentdax/swift,practicalswift/swift,jtbandes/swift,lorentey/swift,kentya6/swift,austinzheng/swift,OscarSwanros/swift,hughbe/swift,stephentyrone/swift,shajrawi/swift,kusl/swift,kusl/swift,aschwaighofer/swift,emilstahl/swift,djwbrown/swift,apple/swift,swiftix/swift.old,lorentey/swift,hooman/swift,mightydeveloper/swift,aschwaighofer/swift,amraboelela/swift,dduan/swift,stephentyrone/swift,hughbe/swift,sdulal/swift,brentdax/swift,tjw/swift,OscarSwanros/swift,swiftix/swift.old,JaSpa/swift,tinysun212/swift-windows,arvedviehweger/swift,gottesmm/swift,swiftix/swift,cbrentharris/swift,shajrawi/swift,uasys/swift,roambotics/swift,slavapestov/swift,Ivacker/swift,MukeshKumarS/Swift,Ivacker/swift,modocache/swift,ahoppen/swift,emilstahl/swift,parkera/swift,huonw/swift,jtbandes/swift,dduan/swift,frootloops/swift,gribozavr/swift,codestergit/swift,karwa/swift,zisko/swift,dduan/swift,CodaFi/swift,alblue/swift,alblue/swift,practicalswift/swift,shajrawi/swift,danielmartin/swift,deyton/swift,shahmishal/swift,mightydeveloper/swift,arvedviehweger/swift,jopamer/swift,allevato/swift,slavapestov/swift,slavapestov/swift,calebd/swift,return/swift,LeoShimonaka/swift,tkremenek/swift,milseman/swift,jtbandes/swift,kentya6/swift,swiftix/swift.old,practicalswift/swift,swiftix/swift,emilstahl/swift,dreamsxin/swift,ken0nek/swift,glessard/swift,IngmarStein/swift,shahmishal/swift,milseman/swift,jckarter/swift,gottesmm/swift,hooman/swift,lorentey/swift,roambotics/swift,felix91gr/swift,KrishMunot/swift,kentya6/swift,ben-ng/swift,khizkhiz/swift,gmilos/swift,aschwaighofer/swift,gmilos/swift,gmilos/swift,JGiola/swift,sdulal/swift,kperryua/swift,kusl/swift,kstaring/swift,felix91gr/swift,jmgc/swift,xwu/swift,IngmarStein/swift,therealbnut/swift,slavapestov/swift,harlanhaskins/swift,OscarSwanros/swift,xwu/swift,benlangmuir/swift,CodaFi/swift,tardieu/swift,ben-ng/swift,milseman/swift,frootloops/swift,Ivacker/swift,nathawes/swift,hooman/swift,CodaFi/swift,xwu/swift,LeoShimonaka/swift,hughbe/swift,johnno1962d/swift,OscarSwanros/swift,SwiftAndroid/swift,Ivacker/swift,uasys/swift,jtbandes/swift,ken0nek/swift,mightydeveloper/swift,frootloops/swift,airspeedswift/swift,shahmishal/swift,jckarter/swift,glessard/swift,gribozavr/swift,MukeshKumarS/Swift,devincoughlin/swift,lorentey/swift,jopamer/swift,tardieu/swift,ahoppen/swift,JaSpa/swift,atrick/swift,sschiau/swift,cbrentharris/swift,kperryua/swift,codestergit/swift,aschwaighofer/swift,JaSpa/swift,karwa/swift,jopamer/swift,arvedviehweger/swift,Jnosh/swift,danielmartin/swift,parkera/swift,modocache/swift,deyton/swift,shajrawi/swift,arvedviehweger/swift,hughbe/swift,Ivacker/swift,kstaring/swift,rudkx/swift,adrfer/swift,hughbe/swift,sschiau/swift,IngmarStein/swift,lorentey/swift,tkremenek/swift,JGiola/swift,apple/swift,tardieu/swift,ken0nek/swift,gmilos/swift,allevato/swift,djwbrown/swift,kusl/swift,khizkhiz/swift,bitjammer/swift,zisko/swift,airspeedswift/swift,frootloops/swift,CodaFi/swift,harlanhaskins/swift,tjw/swift,johnno1962d/swift,gottesmm/swift,jmgc/swift,IngmarStein/swift,codestergit/swift,jtbandes/swift,mightydeveloper/swift,tinysun212/swift-windows,dduan/swift,dduan/swift,kperryua/swift,khizkhiz/swift,karwa/swift,johnno1962d/swift,johnno1962d/swift,benlangmuir/swift,JaSpa/swift,xedin/swift,deyton/swift,ben-ng/swift,MukeshKumarS/Swift,manavgabhawala/swift,russbishop/swift,brentdax/swift,benlangmuir/swift,jckarter/swift,SwiftAndroid/swift,sschiau/swift,LeoShimonaka/swift,milseman/swift,russbishop/swift,huonw/swift,huonw/swift,frootloops/swift,tardieu/swift,gribozavr/swift,stephentyrone/swift,gregomni/swift,codestergit/swift,huonw/swift,nathawes/swift,JaSpa/swift,jopamer/swift,brentdax/swift,gregomni/swift,therealbnut/swift,nathawes/swift,therealbnut/swift,Ivacker/swift,dreamsxin/swift,sschiau/swift,glessard/swift,tkremenek/swift,xedin/swift,IngmarStein/swift,slavapestov/swift,austinzheng/swift,mightydeveloper/swift,ben-ng/swift,natecook1000/swift,bitjammer/swift,karwa/swift,swiftix/swift.old,bitjammer/swift,jtbandes/swift,kentya6/swift,kusl/swift,milseman/swift,khizkhiz/swift,sschiau/swift,felix91gr/swift,LeoShimonaka/swift,felix91gr/swift,jckarter/swift,harlanhaskins/swift,SwiftAndroid/swift,devincoughlin/swift,LeoShimonaka/swift,ben-ng/swift,xedin/swift,kentya6/swift,tjw/swift,kstaring/swift,shahmishal/swift,ha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