install_toolchain: change warn to echo in sudo context

This code runs in sudo context which doesn't have access to common.sh
shell helpers.  Use an echo instead.

BUG=chromium:395265
TEST=setup_board w/injected errors shows the warning message

Change-Id: I12c9cb7ca97d6c09433419e65a478a6d12bf86f2
Reviewed-on: https://chromium-review.googlesource.com/227262
Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/install_toolchain b/install_toolchain
index cd36cdb..5f867cd 100755
--- a/install_toolchain
+++ b/install_toolchain
@@ -123,7 +123,7 @@
       "mkdir -p '${BOARD_ROOT}/usr/lib/debug'"
       "tar jxpf '${libc_path}' -C '${BOARD_ROOT}/usr/lib/debug' \
           './usr/lib/debug/usr/${FLAGS_toolchain}' --strip-components=6 \
-          || warn 'libc debug info not copied.'"
+          || echo 'WARNING: libc debug info not copied.' >&2"
     )
     # TODO(asharif): Remove this hack after a while.
     local board_gcc_dir="${BOARD_ROOT}/usr/lib/gcc"