cc-wrapper, cc-wrapper-old: Simplify shell logic

1. `crossDrv` is now the default so we don't need to worry about that in
   build != host builds.

2. shell is the build time shell, so `wrapCCCross` doesn't need to
   worry, as build == host.

3. `shell.shellPath` will always be appended where useful.

4. Complicated `shell == ""` logic served no purpose.

pkgs/build-support/cc-wrapper/default.nix

@@ -86,7 +86,8 @@ stdenv.mkDerivation {
 
   preferLocalBuild = true;
 
-  inherit cc shell libc_bin libc_dev libc_lib binutils_bin coreutils_bin;
+  inherit cc libc_bin libc_dev libc_lib binutils_bin coreutils_bin;
+  shell = getBin shell + shell.shellPath or "";
   gnugrep_bin = if nativeTools then "" else gnugrep;
 
   binPrefix = prefix;
@@ -384,10 +385,6 @@ stdenv.mkDerivation {
   # for substitution in utils.sh
   expandResponseParams = "${expand-response-params}/bin/expand-response-params";
 
-  crossAttrs = {
-    shell = shell.crossDrv + shell.crossDrv.shellPath;
-  };
-
   meta =
     let cc_ = if cc != null then cc else {}; in
     (if cc_ ? meta then removeAttrs cc.meta ["priority"] else {}) //