c++: fix ICE with -Wduplicated-cond [PR107593]

c++: fix ICE with -Wduplicated-cond [PR107593]

Here we crash because a CAST_EXPR, representing T(), doesn't have
its operand, and operand_equal_p's STRIP_ANY_LOCATION_WRAPPER doesn't
expect that.  (o_e_p is called from warn_duplicated_cond_add_or_warn.)

In the past we've adjusted o_e_p to better cope with template codes,
but in this case I think we just want to avoid attempting to warn
about inst-dependent expressions; I don't think I've ever envisioned
-Wduplicated-cond to warn about them.  Also destroy the chain when
an inst-dependent expression is encountered to not warn in
Wduplicated-cond4.C.

The ICE started with r12-6022, two-stage name lookup for overloaded
operators, which gave dependent operators a TREE_TYPE (in particular,
DEPENDENT_OPERATOR_TYPE), so we no longer bail out here in o_e_p:

  /* Similar, if either does not have a type (like a template id),
     they aren't equal.  */
  if (!TREE_TYPE (arg0) || !TREE_TYPE (arg1))
    return false;

	PR c++/107593
	PR c++/108597

gcc/c-family/ChangeLog:

	* c-common.h (instantiation_dependent_expression_p): Declare.
	* c-warn.cc (warn_duplicated_cond_add_or_warn): If the condition
	is dependent, invalidate the chain.

gcc/c/ChangeLog:

	* c-objc-common.cc (instantiation_dependent_expression_p): New.

gcc/cp/ChangeLog:

	* cp-tree.h (instantiation_dependent_expression_p): Don't
	declare here.

gcc/testsuite/ChangeLog:

	* g++.dg/warn/Wduplicated-cond3.C: New test.
	* g++.dg/warn/Wduplicated-cond4.C: New test.
	* g++.dg/warn/Wduplicated-cond5.C: New test.