[Bug ipa/92606] [11/12/13 Regression][avr] invalid merge of symbols in progmem and data sections

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92606

--- Comment #31 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
This is Maritn's code, but I agree that equals_wpa should reject pairs with
"dangerous" attributes on them (ideally we should hash them). 
I think we could add test for same attributes to equals_wpa and eventually
white list attributes we consider mergeable?
There are attributes that serves no meaning once we enter backend, so it may be
also good option to strip them, so they are not confusing passes like ICF.