[Bug ipa/65502] pure-const should play well with clobbers.

[hubicka at ucw dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65502

--- Comment #5 from Jan Hubicka <hubicka at ucw dot cz> ---
> I think we can safely ignore clobbers when scanning functions for
> pure/constness.

Yes (it is what the patch does), but doing so may cause worse code in the
function calling these destructors.  DCE will remove the destructor call and we
will lose information about memory location being dead.
I think we may want to output the clobber after destructors calls in this case.