build: correct the variable name for cross-compiling
build: correct the variable name for cross-compiling

A typo snuck into the cross-compiling path and due to the machine that it was
tested on hvaing `/bin/llvm-tblgen`, the build succeeded.  Correct the typo to
ensure that we use the correct tblgen.

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