update_chroot: only update toolchains for specific requested board

When we're run via build_packages for a board, don't bother trying to
install every single cross-compiler.  Only pull in the ones this board
actually needs.

TEST=`./setup_board --board=x86-generic` only installs two toolchains

Change-Id: Id20d78987c5fb5b3c9ad024d4f1142273347a6fc
Reviewed-on: https://chromium-review.googlesource.com/229504
Reviewed-by: Bertrand Simonnet <bsimonnet@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
1 file changed