c++: fix initializer_list transformation [PR108071]
In these testcases, we weren't adequately verifying that constructing the
element type from an array element would have the same effect as
constructing it from one of the initializers.
PR c++/108071
PR c++/105838
gcc/cp/ChangeLog:
* call.cc (struct conversion_obstack_sentinel): New.
(maybe_init_list_as_array): Compare conversion of dummy argument.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/initlist131.C: New test.
* g++.dg/cpp0x/initlist132.C: New test.
* g++.dg/cpp0x/initlist133.C: New test.