llvmPackages_*.compiler-rt: use darwinArch

pkgs/development/compilers/llvm/8/compiler-rt.nix

@@ -45,7 +45,7 @@ stdenv.mkDerivation {
     # The compiler-rt build infrastructure sniffs supported platforms on Darwin
     # and finds i386;x86_64;x86_64h. We only build for x86_64, so linking fails
     # when it tries to use libc++ and libc++api for i386.
-    "-DDARWIN_osx_ARCHS=${stdenv.hostPlatform.parsed.cpu.name}"
+    "-DDARWIN_osx_ARCHS=${stdenv.hostPlatform.darwinArch}"
   ];
 
   outputs = [ "out" "dev" ];