[cmake] Fix link pool and allow overriding from command line.
[cmake] Fix link pool and allow overriding from command line.

Fix the usage of JOB_POOL_LINK. JOB_POOL_LINK is not global property,
only a target property. To set in all the targets, one has to set
CMAKE_JOB_POOL_LINK.

Also, allow overriding JOB_POOLS from the command line with
CMAKE_JOB_POOLS. There's a workaround for old versions of CMake which do
not have automatic support for that override.

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