rustc: Fix build

Thanks @jonringer for catching, and sorry I didn't myself!

pkgs/development/compilers/rust/rustc.nix

@@ -88,9 +88,9 @@ in stdenv.mkDerivation rec {
     "${setTarget}.cxx=${cxxForTarget}"
   ] ++ optionals (!withBundledLLVM) [
     "--enable-llvm-link-shared"
-    "${setBuild}.llvm-config=${llvmSharedForBuild}/bin/llvm-config"
-    "${setHost}.llvm-config=${llvmSharedForHost}/bin/llvm-config"
-    "${setTarget}.llvm-config=${llvmSharedForTarget}/bin/llvm-config"
+    "${setBuild}.llvm-config=${llvmSharedForBuild.dev}/bin/llvm-config"
+    "${setHost}.llvm-config=${llvmSharedForHost.dev}/bin/llvm-config"
+    "${setTarget}.llvm-config=${llvmSharedForTarget.dev}/bin/llvm-config"
   ] ++ optionals (stdenv.isLinux && !stdenv.targetPlatform.isRedox) [
     "--enable-profiler" # build libprofiler_builtins
   ] ++ optionals stdenv.buildPlatform.isMusl [