update_chroot: Also update target-sdk-post-cross

Add virtual/target-sdk-post-cross to the list of packages updated by
update_chroot.  This ensures that packages like rust and cargo are
properly updated.

BUG=chromium:820330
TEST=./update_chroot updates rust to 1.24

Change-Id: I5604b91a57b6a3ca4207e6cb1d6dccb6b6d45ad0
Signed-off-by: Chirantan Ekbote <chirantan@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/957936
Reviewed-by: Zach Reizner <zachr@chromium.org>
diff --git a/update_chroot b/update_chroot
index 028b801..ae3d7bc 100755
--- a/update_chroot
+++ b/update_chroot
@@ -122,7 +122,8 @@
 
 # Second pass, update everything else.
 EMERGE_FLAGS+=( --deep )
-sudo -E ${EMERGE_CMD} "${EMERGE_FLAGS[@]}" virtual/target-sdk world
+sudo -E ${EMERGE_CMD} "${EMERGE_FLAGS[@]}" virtual/target-sdk \
+  virtual/target-sdk-post-cross world
 
 # Automatically discard all CONFIG_PROTECT'ed files. Those that are
 # protected should not be overwritten until the variable is changed.