build: only use gold on ELF targets
build: only use gold on ELF targets

gold only supports ELF.  This adds two new helper functions
(is_windows_based_sdk and is_elfish_sdk) to ensure that we dont try to use gold
on non-ELF targets.  This comes up when trying to setup cross-compilation for
the standard library for Windows.

The ELF check is implemented as the negation of Darwin (which uses MachO) and
Windows (which uses COFF).  The reason for this is that there are additional
targets which also use ELF.  Rather than enumerating the larger set, enumerate
the smaller set (windows) and use the negation.

karwa/swift,shajrawi/swift,hooman/swift,Jnosh/swift,xwu/swift,zisko/swift,jtbandes/swift,zisko/swift,stephentyrone/swift,deyton/swift,jopamer/swift,JGiola/swift,kstaring/swift,calebd/swift,xwu/swift,amraboelela/swift,tinysun212/swift-windows,russbishop/swift,therealbnut/swift,atrick/swift,natecook1000/swift,hooman/swift,gottesmm/swift,modocache/swift,manavgabhawala/swift,therealbnut/swift,ben-ng/swift,natecook1000/swift,rudkx/swift,stephentyrone/swift,russbishop/swift,milseman/swift,bitjammer/swift,xedin/swift,kstaring/swift,austinzheng/swift,huonw/swift,manavgabhawala/swift,Jnosh/swift,gribozavr/swift,jtbandes/swift,apple/swift,aschwaighofer/swift,calebd/swift,airspeedswift/swift,alblue/swift,practicalswift/swift,IngmarStein/swift,practicalswift/swift,benlangmuir/swift,gottesmm/swift,tjw/swift,karwa/swift,sschiau/swift,karwa/swift,allevato/swift,nathawes/swift,stephentyrone/swift,therealbnut/swift,IngmarStein/swift,frootloops/swift,tjw/swift,glessard/swift,swiftix/swift,harlanhaskins/swift,natecook1000/swift,atrick/swift,huonw/swift,modocache/swift,allevato/swift,tardieu/swift,harlanhaskins/swift,tjw/swift,milseman/swift,lorentey/swift,return/swift,felix91gr/swift,JaSpa/swift,stephentyrone/swift,jmgc/swift,huonw/swift,uasys/swift,ben-ng/swift,jckarter/swift,amraboelela/swift,jmgc/swift,gribozavr/swift,djwbrown/swift,kperryua/swift,gribozavr/swift,natecook1000/swift,devincoughlin/swift,felix91gr/swift,brentdax/swift,gottesmm/swift,jopamer/swift,swiftix/swift,return/swift,shahmishal/swift,amraboelela/swift,sschiau/swift,allevato/swift,jtbandes/swift,hooman/swift,gmilos/swift,xedin/swift,practicalswift/swift,ahoppen/swift,Jnosh/swift,atrick/swift,devincoughlin/swift,gribozavr/swift,practicalswift/swift,alblue/swift,amraboelela/swift,tkremenek/swift,uasys/swift,kstaring/swift,russbishop/swift,kperryua/swift,JaSpa/swift,nathawes/swift,arvedviehweger/swift,airspeedswift/swift,parkera/swift,tkremenek/swift,aschwaighofer/swift,gottesmm/swift,ahoppen/swift,zisko/swift,hughbe/swift,aschwaighofer/swift,karwa/swift,roambotics/swift,jtbandes/swift,lorentey/swift,frootloops/swift,tinysun212/swift-windows,kperryua/swift,frootloops/swift,gmilos/swift,JGiola/swift,kstaring/swift,austinzheng/swift,calebd/swift,hooman/swift,devincoughlin/swift,tinysun212/swift-windows,tinysun212/swift-windows,roambotics/swift,return/swift,gribozavr/swift,JGiola/swift,roambotics/swift,CodaFi/swift,devincoughlin/swift,alblue/swift,codestergit/swift,brentdax/swift,tjw/swift,jopamer/swift,modocache/swift,modocache/swift,zisko/swift,frootloops/swift,airspeedswift/swift,codestergit/swift,arvedviehweger/swift,allevato/swift,practicalswift/swift,alblue/swift,OscarSwanros/swift,shahmishal/swift,tardieu/swift,sschiau/swift,ben-ng/swift,lorentey/swift,jtbandes/swift,natecook1000/swift,zisko/swift,aschwaighofer/swift,nathawes/swift,bitjammer/swift,Jnosh/swift,stephentyrone/swift,milseman/swift,tjw/swift,gottesmm/swift,tjw/swift,harlanhaskins/swift,swiftix/swift,ahoppen/swift,gmilos/swift,kperryua/swift,bitjammer/swift,uasys/swift,swiftix/swift,practicalswift/swift,shahmishal/swift,manavgabhawala/swift,tardieu/swift,russbishop/swift,codestergit/swift,amraboelela/swift,manavgabhawala/swift,russbishop/swift,danielmartin/swift,uasys/swift,calebd/swift,kstaring/swift,brentdax/swift,jopamer/swift,deyton/swift,shajrawi/swift,codestergit/swift,JGiola/swift,hughbe/swift,xedin/swift,shahmishal/swift,milseman/swift,therealbnut/swift,xwu/swift,CodaFi/swift,calebd/swift,deyton/swift,codestergit/swift,CodaFi/swift,uasys/swift,airspeedswift/swift,milseman/swift,therealbnut/swift,return/swift,aschwaighofer/swift,aschwaighofer/swift,arvedviehweger/swift,parkera/swift,shajrawi/swift,roambotics/swift,parkera/swift,djwbrown/swift,alblue/swift,IngmarStein/swift,IngmarStein/swift,hooman/swift,aschwaighofer/swift,allevato/swift,rudkx/swift,modocache/swift,natecook1000/swift,alblue/swift,harlanhaskins/swift,nathawes/swift,frootloops/swift,nathawes/swift,apple/swift,parkera/swift,parkera/swift,ben-ng/swift,shahmishal/swift,ahoppen/swift,apple/swift,gribozavr/swift,benlangmuir/swift,nathawes/swift,sschiau/swift,devincoughlin/swift,kperryua/swift,huonw/swift,danielmartin/swift,atrick/swift,danielmartin/swift,danielmartin/swift,codestergit/swift,arvedviehweger/swift,xedin/swift,Jnosh/swift,huonw/swift,JaSpa/swift,benlangmuir/swift,calebd/swift,austinzheng/swift,CodaFi/swift,huonw/swift,shajrawi/swift,tkremenek/swift,allevato/swift,JaSpa/swift,rudkx/swift,airspeedswift/swift,jckarter/swift,tinysun212/swift-windows,benlangmuir/swift,manavgabhawala/swift,IngmarStein/swift,rudkx/swift,therealbnut/swift,gregomni/swift,practicalswift/swift,apple/swift,brentdax/swift,ahoppen/swift,glessard/swift,xwu/swift,jckarter/swift,amraboelela/swift,swiftix/swift,hooman/swift,roambotics/swift,jopamer/swift,sschiau/swift,jmgc/swift,deyton/swift,jmgc/swift,brentdax/swift,OscarSwanros/swift,milseman/swift,nathawes/swift,jopamer/swift,deyton/swift,JGiola/swift,bitjammer/swift,gmilos/swift,stephentyrone/swift,ben-ng/swift,jopamer/swift,sschiau/swift,alblue/swift,gregomni/swift,glessard/swift,rudkx/swift,deyton/swift,return/swift,Jnosh/swift,lorentey/swift,djwbrown/swift,swiftix/swift,brentdax/swift,bitjammer/swift,OscarSwanros/swift,tardieu/swift,shajrawi/swift,jckarter/swift,hooman/swift,shahmishal/swift,hughbe/swift,tardieu/swift,austinzheng/swift,atrick/swift,JaSpa/swift,jckarter/swift,kstaring/swift,felix91gr/swift,lorentey/swift,frootloops/swift,JaSpa/swift,return/swift,benlangmuir/swift,gribozavr/swift,russbishop/swift,karwa/swift,parkera/swift,danielmartin/swift,airspeedswift/swift,airspeedswift/swift,hughbe/swift,hughbe/swift,danielmartin/swift,bitjammer/swift,JaSpa/swift,ben-ng/swift,glessard/swift,djwbrown/swift,shahmishal/swift,swiftix/swift,apple/swift,jtbandes/swift,tkremenek/swift,OscarSwanros/swift,djwbrown/swift,codestergit/swift,danielmartin/swift,jckarter/swift,tkremenek/swift,manavgabhawala/swift,hughbe/swift,sschiau/swift,apple/swift,jckarter/swift,return/swift,xwu/swift,xwu/swift,arvedviehweger/swift,felix91gr/swift,hughbe/swift,gottesmm/swift,gregomni/swift,gottesmm/swift,uasys/swift,tjw/swift,atrick/swift,manavgabhawala/swift,gmilos/swift,felix91gr/swift,brentdax/swift,parkera/swift,austinzheng/swift,gmilos/swift,Jnosh/swift,OscarSwanros/swift,practicalswift/swift,CodaFi/swift,gregomni/swift,zisko/swift,devincoughlin/swift,tinysun212/swift-windows,sschiau/swift,roambotics/swift,JGiola/swift,tardieu/swift,jtbandes/swift,stephentyrone/swift,shajrawi/swift,lorentey/swift,shajrawi/swift,CodaFi/swift,parkera/swift,gregomni/swift,karwa/swift,rudkx/swift,harlanhaskins/swift,shajrawi/swift,natecook1000/swift,shahmishal/swift,bitjammer/swift,glessard/swift,gmilos/swift,tardieu/swift,OscarSwanros/swift,felix91gr/swift,jmgc/swift,gregomni/swift,CodaFi/swift,kperryua/swift,tinysun212/swift-windows,modocache/swift,amraboelela/swift,djwbrown/swift,allevato/swift,calebd/swift,karwa/swift,tkremenek/swift,modocache/swift,arvedviehweger/swift,zisko/swift,kstaring/swift,huonw/swift,xedin/swift,jmgc/swift,harlanhaskins/swift,therealbnut/swift,uasys/swift,xedin/swift,djwbrown/swift,gribozavr/swift,devincoughlin/swift,austinzheng/swift,devincoughlin/swift,lorentey/swift,OscarSwanros/swift,russbishop/swift,jmgc/swift,kperryua/swift,xedin/swift,IngmarStein/swift,ahoppen/swift,xedin/swift,deyton/swift,lorentey/swift,xwu/swift,austinzheng/swift,ben-ng/swift,benlangmuir/swift,IngmarStein/swift,karwa/swift,felix91gr/swift,arvedviehweger/swift,glessard/swift,harlanhaskins/swift,milseman/swift,frootloops/swift,tkremenek/swift