[CMake] Use NO_CMAKE_FIND_ROOT_PATH for LLVM and clang
[CMake] Use NO_CMAKE_FIND_ROOT_PATH for LLVM and clang

When cross-compiling or specifying a custom sysroot and desiring a
hermetic build, many CMake toolchain files will have a custom
CMAKE_FIND_ROOT_PATH and set the CMAKE_FIND_ROOT_PATH_MODE_* variables
to ONLY, meaning packages will only be searched for in the rerooted
directories. We don't want this rerooting to happen when searching for
the LLVM and clang packages though, since we're specifying our search
paths explicitly and excluding search paths from the system, and we
don't want those explicit search paths to be rerooted.

It's standard to set CMAKE_FIND_ROOT_PATH_MODE_PROGRAM to NEVER instead
of ONLY, since you usually want programs to be found for the build
system and not the host system, so the change for the llvm-config search
is not technically required. It doesn't hurt for consistency though, and
I can envision some scenarios in which it might come in handy.

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