ART: Generate chained compare-and-branch for short switches

Refactor Mir2Lir to generate chained compare-and-branch sequences
for short switches on all architectures.

Change-Id: Ie2a572ae69d462ba68a119e9fb93ae538cddd08f
diff --git a/test/015-switch/expected.txt b/test/015-switch/expected.txt
index ca3b518..91b4714 100644
--- a/test/015-switch/expected.txt
+++ b/test/015-switch/expected.txt
@@ -8,3 +8,9 @@
 CORRECT (default only)
 CORRECT big sparse / first
 CORRECT big sparse / last
+default
+254
+255
+256
+257
+default