stdenv: Store one package per line in nix-support/propagated-*

This makes those files a bit easier to read. Also, for what it's worth,
it brings us one baby step closer to handling spaces in store paths.

Also, I optimized handling of many transitive deps with read. Probably,
not very beneficial, but nice to enforce the pkg-per-line structure.
Doing so let me find much dubious code and fix it.

Two misc notes:

 - `propagated-user-env-packages` also needed to be adjusted as
   sometimes it is copied to/from the propagated input files.

 - `local fd` should ensure that file descriptors aren't clobbered
   during recursion.

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

@@ -275,9 +275,9 @@ stdenv.mkDerivation {
       # Propagate the wrapped cc so that if you install the wrapper,
       # you get tools like gcov, the manpages, etc. as well (including
       # for binutils and Glibc).
-      echo ${cc} ${cc.man or ""} ${binutils_bin} ${if libc == null then "" else libc_bin} > $out/nix-support/propagated-user-env-packages
+      printLines ${cc} ${cc.man or ""} ${binutils_bin} ${if libc == null then "" else libc_bin} > $out/nix-support/propagated-user-env-packages
 
-      echo ${toString extraPackages} > $out/nix-support/propagated-native-build-inputs
+      printLines ${toString extraPackages} > $out/nix-support/propagated-native-build-inputs
     ''
 
     + optionalString (targetPlatform.isSunOS && nativePrefix != "") ''