setup_board: look up sdk targets only

We don't care about non-sdk targets when setting up the host boards,
so only load those for processing.

BUG=None
TEST=`cbuildbot chromiumos-sdk` passed

Change-Id: Ifa0f82a8c9704862a714fd9f35cbd11d809e295f
Reviewed-on: https://gerrit.chromium.org/gerrit/25626
Reviewed-by: Zdenek Behan <zbehan@chromium.org>
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/setup_board b/setup_board
index 7c502fc..d7cd3c7 100755
--- a/setup_board
+++ b/setup_board
@@ -553,7 +553,7 @@
   # The new chroot should have gcc for each target. Make sure that
   # the latest one is correctly selected. Ignore cat errors as not
   # all overlays will have a toolchain.conf.
-  ALL_TARGETS=$(cros_setup_toolchains --show-board-cfg=all)
+  ALL_TARGETS=$(cros_setup_toolchains --show-board-cfg=sdk)
   for target in ${ALL_TARGETS//,/ }; do
     libc=$(eval $(crossdev --show-target-cfg "${target}"); echo ${libc_pn})
     if [[ ${libc} == "glibc" ]] ; then