c++: constexpr and volatile member function [PR80456]

c++: constexpr and volatile member function [PR80456]

When calling a static member function we still need to evaluate an explicit
object argument.  But we don't want to force a load of the entire object
if the argument is volatile, so we take its address.  If as a result it no
longer has any side-effects, we don't need to evaluate it after all.

gcc/cp/ChangeLog:

	PR c++/80456
	* call.c (build_new_method_call_1): Check again for side-effects
	with a volatile object.

gcc/testsuite/ChangeLog:

	PR c++/80456
	* g++.dg/cpp0x/constexpr-volatile3.C: New test.