test/decode: Add tests for PatternGroups

This adds one test that supposed to succeed to test deep nesting
of pattern groups which is rarely exercised by targets using decode
tree. The remaining tests exercise various fail conditions.

Signed-off-by: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
Message-Id: <20190227120217.20794-1-kbastian@mail.uni-paderborn.de>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

tests/decode/err_pattern_group_empty.decode

@@ -0,0 +1,6 @@
+# This work is licensed under the terms of the GNU LGPL, version 2 or later.
+# See the COPYING.LIB file in the top-level directory.
+
+# empty groups are not allowed
+{
+}