Fix inter-procedural EAF flags propagation with respect to !binds_to_current_def_p

Fix inter-procedural EAF flags propagation with respect to !binds_to_current_def_p

While proofreading the code for handling EAF flags of !binds_to_current_def_p I
noticed that the interprocedural dataflow actually ignores the flag possibly
introducing wrong code on quite complex interposable functions in non-trivial
recursion cycles (or at ltrans partition boundary).

This patch unifies the flags changes to single place (remove_useless_eaf_flags)
and does extend modref_merge_call_site_flags to do the right thing.

lto-bootstrapped/regtested x86_64-linux.  Plan to commit it today after bit
more testing (firefox/clang build).

gcc/ChangeLog:

	* gimple.c (gimple_call_arg_flags): Use interposable_eaf_flags.
	(gimple_call_retslot_flags): Likewise.
	(gimple_call_static_chain_flags): Likewise.
	* ipa-modref.c (remove_useless_eaf_flags): Do not remove everything for
	NOVOPS.
	(modref_summary::useful_p): Likewise.
	(modref_summary_lto::useful_p): Likewise.
	(analyze_parms): Do not give up on NOVOPS.
	(analyze_function): When dumping report chnages in EAF flags
	between IPA and local pass.
	(modref_merge_call_site_flags): Compute implicit eaf flags
	based on callee ecf_flags and fnspec; if the function does not
	bind to current defs use interposable_eaf_flags.
	(modref_propagate_flags_in_scc): Update.
	* ipa-modref.h (interposable_eaf_flags): New function.