c++: Extend -Wpessimizing-move to other contexts

c++: Extend -Wpessimizing-move to other contexts

In my recent patch which enhanced -Wpessimizing-move so that it warns
about class prvalues too I said that I'd like to extend it so that it
warns in more contexts where a std::move can prevent copy elision, such
as:

  T t = std::move(T());
  T t(std::move(T()));
  T t{std::move(T())};
  T t = {std::move(T())};
  void foo (T);
  foo (std::move(T()));

This patch does that by adding two maybe_warn_pessimizing_move calls.
These must happen before we've converted the initializers otherwise the
std::move will be buried in a TARGET_EXPR.

	PR c++/106276

gcc/cp/ChangeLog:

	* call.cc (build_over_call): Call maybe_warn_pessimizing_move.
	* cp-tree.h (maybe_warn_pessimizing_move): Declare.
	* decl.cc (build_aggr_init_full_exprs): Call
	maybe_warn_pessimizing_move.
	* typeck.cc (maybe_warn_pessimizing_move): Handle TREE_LIST and
	CONSTRUCTOR.  Add a bool parameter and use it.  Adjust a diagnostic
	message.
	(check_return_expr): Adjust the call to maybe_warn_pessimizing_move.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/Wpessimizing-move7.C: Add dg-warning.
	* g++.dg/cpp0x/Wpessimizing-move8.C: New test.