ipa/122456 - fix ICE during LTO profiledbootstrap

ipa/122456 - fix ICE during LTO profiledbootstrap

When we have a speculated edge but we folded the call to
__builtin_unreachable () then trying to update the cgraph ICEs
in resolve_speculation because there's no symtab node for
__builtin_unreachable (). Reject this resolving attempt similar
as to when the callees decl were NULL or it were not semantically
equivalent.

I only have a LTRANS unit as testcase.

	PR ipa/122456
	* cgraph.cc (cgraph_edge::resolve_speculation): Handle
	a NULL symtab_node::get (callee_decl).