Extend modref by side-effect analysis

Make modref to also collect info whether function has side
effects.  This allows pure/const function detection and also handling
functions which do store some memory in similar way as we handle
pure/consts now.

The code is symmetric to what ipa-pure-const does.  Modref is actually more
capable on proving that a given function is pure/const (since it understands
that non-pure function can be called when it only modifies data on stack)
so we could retire ipa-pure-const's pure-const discovery at some point.

However this patch only does the anlaysis - the consumers of this flag
will come next.

Bootstrapped/regtested x86_64-linux. I plan to commit it later today
if there are no complains.

gcc/ChangeLog:

	* ipa-modref.c: Include tree-eh.h
	(modref_summary::modref_summary): Initialize side_effects.
	(struct modref_summary_lto): New bool field side_effects.
	(modref_summary_lto::modref_summary_lto): Initialize side_effects.
	(modref_summary::dump): Dump side_effects.
	(modref_summary_lto::dump): Dump side_effects.
	(merge_call_side_effects): Merge side effects.
	(process_fnspec): Calls to non-const/pure or looping
	function is a side effect.
	(analyze_call): Self-recursion is a side-effect; handle
	special builtins.
	(analyze_load): Watch for volatile and throwing memory.
	(analyze_store): Likewise.
	(analyze_stmt): Watch for volatitle asm.
	(analyze_function): Handle side_effects.
	(modref_summaries::duplicate): Duplicate side_effects.
	(modref_summaries_lto::duplicate): Likewise.
	(modref_write): Stream side_effects.
	(read_section): Likewise.
	(update_signature): Update.
	(propagate_unknown_call): Handle side_effects.
	(modref_propagate_in_scc): Likewise.
	* ipa-modref.h (struct modref_summary): Add side_effects.
	* ipa-pure-const.c (special_builtin_state): Rename to ...
	(builtin_safe_for_const_function_p): ... this one.
	(check_call): Update.
	(finite_function_p): Break out from ...
	(propagate_pure_const): ... here
	* ipa-utils.h (finite_function): Declare.

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