util/release/build-release: Create cross-toolchain version file

Add cross-toolchain version file to the release tarball, which can be
used for pre-setting the variables used in buildgcc.

Change-Id: Iad1e0adaa95b71f161caf978276bfb0a63eac8f4
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/58399
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

util/release/build-release

@@ -57,6 +57,8 @@ if [ -n "$COMMIT_ID" ]; then
 	git reset --hard "$COMMIT_ID"
 fi
 
+util/crossgcc/buildgcc -W > .crossgcc-version
+
 git submodule update --init --checkout
 if [ -n "$GPG_KEY_ID" ]; then
 	git tag -a -s -u "$GPG_KEY_ID" --force "$VERSION_NAME" -m "coreboot version $VERSION_NAME"