runInLinuxVM: minimize saved-env

The export to saved-env was very intentionally done at the very
beginning of vmRunCommand, even jumping through extra hoops just to
avoid the PATH variable from polluting the saved variable.

In 26eba25 we loaded stdenv in the
wrong place, we should do it after saving the previous environment. This
is also more consistent with the order of how we load those values back
in stage2Init.

Author: wolfgangwalther

pkgs/build-support/vm/default.nix

@@ -230,11 +230,11 @@ rec {
 
 
   vmRunCommand = qemuCommand: writeText "vm-run" ''
+    export > saved-env
     if [ -f "''${NIX_ATTRS_SH_FILE-}" ]; then
       source "$NIX_ATTRS_SH_FILE"
     fi
     source $stdenv/setup
-    export > saved-env
 
     PATH=${coreutils}/bin
     mkdir xchg