crossgcc/Dockerfile: Add gnat to build the Ada toolchain

If gnat is installed, buildgcc automatically enables Ada support.
Instead of the general `gnat` package we install `gnat-6` which saves
us about 80 MiB of downloads of unused "dependencies".

Change-Id: Ie0b8564d016d458cd33ff75a2ee7bbd5de33afe2
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/18772
Tested-by: build bot (Jenkins)
Reviewed-by: Philippe Mathieu-Daudé <philippe.mathieu.daude@gmail.com>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Martin Roth <martinroth@google.com>

0 files changed, 0 insertions, 0 deletions