re PR ipa/61602 (ICE in lto1 on x86_64-linux-gnu in ipa_single_use, at ipa.c:1257)
PR ipa/61602
* gcc.dg/torture/pr61602.c: New testcase.
* cgraph.h (ipa_discover_readonly_nonaddressable_vars): Return bool.
* ipa.c (set_writeonly_bit): Track if reference was removed.
(ipa_discover_readonly_nonaddressable_vars): Return true if any
references was removed.
* ipa-reference.c (propagate): Return TODO_remove_functions if
reference was removed.