c++: initializer_list<string> and EH [PR114935]

c++: initializer_list<string> and EH [PR114935]

When we initialize an array of a type with a non-trivial destructor, such as
the backing array for the initializer_list, we have a cleanup to destroy any
constructed elements if a later constructor throws.  When the array being
created is a variable, the end of that EH region naturally coincides with
the beginning of the EH region for the cleanup for the variable as a whole.

But if the array is a temporary, or a subobject of one, the array cleanup
region lasts for the rest of the full-expression, along with the normal
cleanup for the TARGET_EXPR.  As a result, when tata throws we clean it up
twice.  Before r14-1705 we avoided this by disabling the array cleanup in
split_nonconstant_init, but after that we don't go through
split_nonconstant_init, so let's handle it in cp_genericize_target_expr.

	PR c++/114935

gcc/cp/ChangeLog:

	* cp-gimplify.cc (cp_genericize_init): Add flags parm.
	(cp_genericize_init_expr): Pass nullptr.
	(cp_genericize_target_expr): Handle cleanup flags.
	* typeck2.cc (build_disable_temp_cleanup): Factor out of...
	(split_nonconstant_init): ...here.
	* cp-tree.h (build_disable_temp_cleanup): Declare.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/initlist-eh1.C: New test.