Merge 'staging' into closure-size

This is mainly to get the update of bootstrap tools.
Otherwise there were mysterious segfaults:
https://github.com/NixOS/nixpkgs/pull/7701#issuecomment-203389817

pkgs/stdenv/generic/setup.sh

@@ -649,14 +649,14 @@ configurePhase() {
 
     # Add --disable-dependency-tracking to speed up some builds.
     if [ -z "$dontAddDisableDepTrack" ]; then
-        if grep -q dependency-tracking "$configureScript"; then
+        if [ -f "$configureScript" ] && grep -q dependency-tracking "$configureScript"; then
             configureFlags="--disable-dependency-tracking $configureFlags"
         fi
     fi
 
     # By default, disable static builds.
     if [ -z "$dontDisableStatic" ]; then
-        if grep -q enable-static "$configureScript"; then
+        if [ -f "$configureScript" ] && grep -q enable-static "$configureScript"; then
             configureFlags="--disable-static $configureFlags"
         fi
     fi