Libdw: Fix build on 32-bit platforms
Libdw: Fix build on 32-bit platforms

The casting here is a bit tricky since Dwarf_Addr is always 64-bits.
This means we first need to narrow to uintptr_t before casting to/from a
pointer for compatibility on 32-bit architectures.

shlevy/ghc,gridaphobe/ghc,shlevy/ghc,GaloisInc/halvm-ghc,gridaphobe/ghc,snoyberg/ghc,sdiehl/ghc,vikraman/ghc,vTurbine/ghc,vikraman/ghc,ezyang/ghc,mettekou/ghc,mettekou/ghc,sgillespie/ghc,GaloisInc/halvm-ghc,shlevy/ghc,ezyang/ghc,mcschroeder/ghc,tjakway/ghcjvm,ezyang/ghc,sdiehl/ghc,mettekou/ghc,mcschroeder/ghc,snoyberg/ghc,mettekou/ghc,gridaphobe/ghc,vTurbine/ghc,sgillespie/ghc,olsner/ghc,sgillespie/ghc,olsner/ghc,gridaphobe/ghc,sgillespie/ghc,sdiehl/ghc,tjakway/ghcjvm,vikraman/ghc,mcschroeder/ghc,oldmanmike/ghc,vikraman/ghc,snoyberg/ghc,nushio3/ghc,olsner/ghc,vikraman/ghc,GaloisInc/halvm-ghc,sdiehl/ghc,tjakway/ghcjvm,mcschroeder/ghc,snoyberg/ghc,gridaphobe/ghc,oldmanmike/ghc,ezyang/ghc,olsner/ghc,oldmanmike/ghc,tjakway/ghcjvm,ezyang/ghc,nushio3/ghc,shlevy/ghc,snoyberg/ghc,sgillespie/ghc,gridaphobe/ghc,oldmanmike/ghc,sgillespie/ghc,mcschroeder/ghc,vikraman/ghc,olsner/ghc,vTurbine/ghc,sdiehl/ghc,mettekou/ghc,shlevy/ghc,nushio3/ghc,vikraman/ghc,nushio3/ghc,GaloisInc/halvm-ghc,mcschroeder/ghc,vTurbine/ghc,vTurbine/ghc,sgillespie/ghc,ezyang/ghc,oldmanmike/ghc,GaloisInc/halvm-ghc,mettekou/ghc,shlevy/ghc,oldmanmike/ghc,tjakway/ghcjvm,mcschroeder/ghc,tjakway/ghcjvm,olsner/ghc,vTurbine/ghc,snoyberg/ghc,nushio3/ghc,vTurbine/ghc,mettekou/ghc,tjakway/ghcjvm,GaloisInc/halvm-ghc,sdiehl/ghc,ezyang/ghc,gridaphobe/ghc,olsner/ghc,shlevy/ghc,sdiehl/ghc,oldmanmike/ghc,nushio3/ghc,nushio3/ghc,GaloisInc/halvm-ghc,snoyberg/ghc