build: do not touch `CMAKE_C_FLAGS` and `CMAKE_CXX_FLAGS`
build: do not touch `CMAKE_C_FLAGS` and `CMAKE_CXX_FLAGS`

Use the appropriate CMake functions to adjust the build flags rather
than touching the user-controlled `CMAKE_C_FLAGS` and `CMAKE_CXX_FLAGS`.

airspeedswift/swift,parkera/swift,aschwaighofer/swift,benlangmuir/swift,nathawes/swift,ahoppen/swift,nathawes/swift,benlangmuir/swift,stephentyrone/swift,stephentyrone/swift,CodaFi/swift,nathawes/swift,tkremenek/swift,xwu/swift,CodaFi/swift,atrick/swift,allevato/swift,apple/swift,xwu/swift,xedin/swift,atrick/swift,lorentey/swift,shahmishal/swift,devincoughlin/swift,tkremenek/swift,xedin/swift,hooman/swift,jckarter/swift,ahoppen/swift,rudkx/swift,jckarter/swift,karwa/swift,stephentyrone/swift,glessard/swift,aschwaighofer/swift,rudkx/swift,roambotics/swift,devincoughlin/swift,atrick/swift,hooman/swift,gribozavr/swift,rudkx/swift,allevato/swift,gribozavr/swift,gribozavr/swift,stephentyrone/swift,benlangmuir/swift,JGiola/swift,sschiau/swift,xwu/swift,parkera/swift,stephentyrone/swift,shahmishal/swift,CodaFi/swift,stephentyrone/swift,lorentey/swift,karwa/swift,devincoughlin/swift,CodaFi/swift,CodaFi/swift,jmgc/swift,karwa/swift,roambotics/swift,atrick/swift,benlangmuir/swift,airspeedswift/swift,hooman/swift,lorentey/swift,jckarter/swift,shahmishal/swift,sschiau/swift,shahmishal/swift,apple/swift,roambotics/swift,jmgc/swift,nathawes/swift,xedin/swift,shahmishal/swift,ahoppen/swift,sschiau/swift,airspeedswift/swift,sschiau/swift,jmgc/swift,gribozavr/swift,parkera/swift,glessard/swift,allevato/swift,karwa/swift,apple/swift,karwa/swift,shahmishal/swift,harlanhaskins/swift,CodaFi/swift,airspeedswift/swift,glessard/swift,harlanhaskins/swift,jmgc/swift,jmgc/swift,gregomni/swift,allevato/swift,jckarter/swift,karwa/swift,sschiau/swift,xwu/swift,lorentey/swift,karwa/swift,aschwaighofer/swift,aschwaighofer/swift,harlanhaskins/swift,xedin/swift,ahoppen/swift,CodaFi/swift,roambotics/swift,jckarter/swift,atrick/swift,jmgc/swift,gribozavr/swift,JGiola/swift,JGiola/swift,devincoughlin/swift,JGiola/swift,allevato/swift,tkremenek/swift,airspeedswift/swift,gregomni/swift,lorentey/swift,sschiau/swift,tkremenek/swift,parkera/swift,jckarter/swift,nathawes/swift,gregomni/swift,devincoughlin/swift,stephentyrone/swift,devincoughlin/swift,xwu/swift,benlangmuir/swift,parkera/swift,xedin/swift,harlanhaskins/swift,ahoppen/swift,apple/swift,gribozavr/swift,gribozavr/swift,allevato/swift,hooman/swift,aschwaighofer/swift,harlanhaskins/swift,atrick/swift,xwu/swift,rudkx/swift,xedin/swift,roambotics/swift,shahmishal/swift,jmgc/swift,hooman/swift,shahmishal/swift,glessard/swift,gregomni/swift,aschwaighofer/swift,xwu/swift,airspeedswift/swift,rudkx/swift,sschiau/swift,JGiola/swift,sschiau/swift,harlanhaskins/swift,lorentey/swift,JGiola/swift,parkera/swift,allevato/swift,parkera/swift,tkremenek/swift,tkremenek/swift,gregomni/swift,apple/swift,parkera/swift,harlanhaskins/swift,nathawes/swift,glessard/swift,roambotics/swift,glessard/swift,karwa/swift,tkremenek/swift,nathawes/swift,devincoughlin/swift,gregomni/swift,airspeedswift/swift,xedin/swift,lorentey/swift,ahoppen/swift,benlangmuir/swift,gribozavr/swift,aschwaighofer/swift,hooman/swift,rudkx/swift,jckarter/swift,apple/swift,lorentey/swift,hooman/swift,devincoughlin/swift,xedin/swift