reorganize crossDrv hooks

pkgs/development/libraries/glibc/default.nix

@@ -40,7 +40,7 @@ in
     # Building from a proper gcc staying in the path where it was installed,
     # libgcc_s will not be at {gcc}/lib, and gcc's libgcc will be found without
     # any special hack.
-    preInstall = if cross != null then "" else ''
+    preInstall = ''
       if [ -f ${stdenv.cc.cc}/lib/libgcc_s.so.1 ]; then
           mkdir -p $out/lib
           cp ${stdenv.cc.cc}/lib/libgcc_s.so.1 $out/lib/libgcc_s.so.1
@@ -114,6 +114,10 @@ in
         dontStrip=1
       '';
 
+      preInstall = null; # clobber the native hook
+
+      separateDebugInfo = false; # this is currently broken for crossDrv
+
       # To avoid a dependency on the build system 'bash'.
       preFixup = ''
         rm $bin/bin/{ldd,tzselect,catchsegv,xtrace}