build: use the target variables for the ICU check
build: use the target variables for the ICU check

The ICU library is used for the target library, not the host tools.  Use the
appropriate variable `SWIFT_PRIMARY_VARIANT_SDK` and
`SWIFT_PRIMARY_VARIANT_ARCH` to select the right CMake variables for the ICU
definitions.  There is no need to use the `_default` suffixed versions as the
defaults have already been used to set the value above.

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