cros_setup_toolchain: Munge the shebang back to use "env"

In CL:719258 we're optimizing the shebang of the toolchain wrappers.
...but we can't necessarily use this optimized version outside the
chroot.  Munge it back.

BUG=chromium:773138
TEST=See that things get munged back

Change-Id: I08e280bca46cd2f36049502cd87466d4f581895f
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/719719
Reviewed-by: Manoj Gupta <manojgupta@chromium.org>
diff --git a/scripts/cros_setup_toolchains.py b/scripts/cros_setup_toolchains.py
index 9b5a412..27708dd 100644
--- a/scripts/cros_setup_toolchains.py
+++ b/scripts/cros_setup_toolchains.py
@@ -1115,6 +1115,13 @@
   for sysroot_wrapper in glob.glob(os.path.join(
       output_dir + srcpath, 'sysroot_wrapper*')):
     contents = osutils.ReadFile(sysroot_wrapper).splitlines()
+
+    # In order to optimize startup time in the chroot we run python a little
+    # differently there.  Put it back to the more portable way here.
+    # See http://crbug.com/773138 for some details.
+    if contents[0] == '#!/usr/bin/python2 -S':
+      contents[0] = '#!/usr/bin/env python2'
+
     for num in xrange(len(contents)):
       if '@CCACHE_DEFAULT@' in contents[num]:
         assert 'True' in contents[num]