c++: ICE with ptr-to-member-fn [PR119344]

c++: ICE with ptr-to-member-fn [PR119344]

This ICE appeared with the removal of NON_DEPENDENT_EXPR.  Previously
skip_simple_arithmetic would get NON_DEPENDENT_EXPR<CAST_EXPR<>> and
since NON_DEPENDENT_EXPR is neither BINARY_CLASS_P nor UNARY_CLASS_P,
there was no problem.  But now we pass just CAST_EXPR<> and a CAST_EXPR
is a tcc_unary, so we extract its null operand and crash.

skip_simple_arithmetic is called from save_expr.  cp_save_expr already
avoids calling save_expr in a template, so that seems like an appropriate
way to fix this.

	PR c++/119344

gcc/cp/ChangeLog:

	* typeck.cc (cp_build_binary_op): Use cp_save_expr instead of save_expr.

gcc/testsuite/ChangeLog:

	* g++.dg/conversion/ptrmem10.C: New test.

Reviewed-by: Patrick Palka <ppalka@redhat.com>
Reviewed-by: Jason Merrill <jason@redhat.com>