tests/docker: add a test-tcg for building then running check-tcg

This is mostly useful for verifying containers will work on the CI
setup.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20210305092328.31792-4-alex.bennee@linaro.org>

tests/docker/test-tcg

+#!/bin/bash -e
+#
+# Build and run the TCG tests
+#
+# Copyright (c) 2021 Linaro Ltd.
+#
+# Authors:
+#  Alex Bennée <alex.bennee@linaro.org>
+#
+# This work is licensed under the terms of the GNU GPL, version 2
+# or (at your option) any later version. See the COPYING file in
+# the top-level directory.
+
+. common.rc
+
+cd "$BUILD_DIR"
+
+# although we are not building QEMU itself we still need a configured
+# build for the unit tests to be built and run
+TARGET_LIST=${TARGET_LIST:-$DEF_TARGET_LIST} \
+build_qemu
+check_qemu check-tcg