Added next condition check to branch instruction

Since branch 'b' instructions currently do not support being part of
an it block, I added a dcheck to the branch instruction in the Thumb2
assembler to ensure that the instruction is not part of an it block.

Change-Id: Ie09f687906add471274a4029cb59a7d90b5feba4
diff --git a/compiler/utils/arm/assembler_thumb2.cc b/compiler/utils/arm/assembler_thumb2.cc
index f9e1ac6..61137c9 100644
--- a/compiler/utils/arm/assembler_thumb2.cc
+++ b/compiler/utils/arm/assembler_thumb2.cc
@@ -975,6 +975,7 @@
 }
 
 void Thumb2Assembler::b(Label* label, Condition cond) {
+  DCHECK_EQ(next_condition_, AL);
   EmitBranch(cond, label, false, false);
 }