c++: assignment to temporary [PR59950]

Given build_this of a TARGET_EXPR, cp_build_fold_indirect_ref returns the
TARGET_EXPR.  But that's the wrong value category for the result of the
defaulted class assignment operator, which returns an lvalue, so we need to
actually build the INDIRECT_REF.

	PR c++/59950

gcc/cp/ChangeLog:

	* call.cc (build_over_call): Use cp_build_indirect_ref.

gcc/testsuite/ChangeLog:

	* g++.dg/init/assign2.C: New test.

gcc/cp/call.cc

@@ -9789,7 +9789,10 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
 	   && DECL_OVERLOADED_OPERATOR_IS (fn, NOP_EXPR)
 	   && trivial_fn_p (fn))
     {
-      tree to = cp_build_fold_indirect_ref (argarray[0]);
+      /* Don't use cp_build_fold_indirect_ref, op= returns an lvalue even if
+	 the object argument isn't one.  */
+      tree to = cp_build_indirect_ref (input_location, argarray[0],
+				       RO_ARROW, complain);
       tree type = TREE_TYPE (to);
       tree as_base = CLASSTYPE_AS_BASE (type);
       tree arg = argarray[1];

gcc/testsuite/g++.dg/init/assign2.C

@@ -0,0 +1,6 @@
+// PR c++/59950
+
+ struct Foo {};
+
+ int f(Foo *p);
+ int n = f(&(Foo() = Foo()));