util/crossgcc: Add empty directory for tarballs

A directory for tarballs is needed in any case but it's created at build
time. However, in reproducible build environments the sources are
downloaded before the buildgcc scripts runs and the directory needs to
be created.

Thus, to simplify that, add an empty tarballs directory.

Change-Id: Id3b4bf918c93f10c145f580684e916a4f8bae3b1
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/75273
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
diff --git a/util/crossgcc/tarballs/.empty b/util/crossgcc/tarballs/.empty
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/util/crossgcc/tarballs/.empty