The problem in this testcase is that the front end expects an rvalue
COND_EXPR to initialize a single temporary from one of the arms.  But
because gimplify_cond_expr used MODIFY_EXPR, instead the arms would each
create their own temporary and then copy that into the common temporary.

So, let's use INIT_EXPR instead.

	* gimplify.c (gimplify_cond_expr): Use INIT_EXPR.

From-SVN: r269403