Improve some error messages.

ll.py

@@ -77,7 +77,7 @@ def ty2s(ty):
         return ty2s(ty.inner_ty) + '*'
     else:
         # TODO
-        print('Unknown type: {}'
+        print('ty2s: Unknown type: {}'
               .format(ty))
         return str(ty)
 
@@ -89,7 +89,7 @@ def oper2s(operand):
         return '%' + operand.val
     else:
         # TODO
-        print('Unknown operand: {}'
+        print('oper2s: Unknown operand: {}'
               .format(operand))
 
 
@@ -104,5 +104,5 @@ def insn2s(insn):
                         oper2s(insn.left), oper2s(insn.right)))
     else:
         # TODO
-        print('Unknown insn: {}'
+        print('insn2s: Unknown insn: {}'
               .format(insn))