runtime: enable shims for Float16 on Windows (x86)
runtime: enable shims for Float16 on Windows (x86)

When building for Windows x86, we do not have `__i686__` defined, but do
have `__i386__` defined.  Ensure that the routines are included for the
x86 Windows target.

benlangmuir/swift,glessard/swift,atrick/swift,glessard/swift,gregomni/swift,hooman/swift,JGiola/swift,roambotics/swift,xwu/swift,jmgc/swift,jmgc/swift,benlangmuir/swift,apple/swift,apple/swift,gregomni/swift,roambotics/swift,apple/swift,parkera/swift,atrick/swift,benlangmuir/swift,parkera/swift,hooman/swift,jmgc/swift,xwu/swift,rudkx/swift,rudkx/swift,glessard/swift,ahoppen/swift,parkera/swift,JGiola/swift,jmgc/swift,ahoppen/swift,roambotics/swift,hooman/swift,glessard/swift,gregomni/swift,ahoppen/swift,rudkx/swift,benlangmuir/swift,tkremenek/swift,roambotics/swift,hooman/swift,jmgc/swift,jmgc/swift,parkera/swift,xwu/swift,JGiola/swift,ahoppen/swift,JGiola/swift,glessard/swift,tkremenek/swift,xwu/swift,hooman/swift,apple/swift,rudkx/swift,apple/swift,rudkx/swift,xwu/swift,parkera/swift,hooman/swift,glessard/swift,JGiola/swift,roambotics/swift,tkremenek/swift,ahoppen/swift,tkremenek/swift,jmgc/swift,parkera/swift,benlangmuir/swift,atrick/swift,gregomni/swift,tkremenek/swift,xwu/swift,atrick/swift,xwu/swift,tkremenek/swift,parkera/swift,parkera/swift,gregomni/swift,roambotics/swift,benlangmuir/swift,gregomni/swift,atrick/swift,tkremenek/swift,atrick/swift,rudkx/swift,apple/swift,hooman/swift,ahoppen/swift,JGiola/swift