abg-ir.cc: Improve types_have_similar_structure.

abg-ir.cc: Improve types_have_similar_structure.

This function is used to determine whether or not type differences are
"local" and is primarily used in --leaf-changes-only mode. The logic
has some issues which are addressed by this patch:

    - Any number of points-to (*) and refers-to (& and &&) components
      are peeled off the types being compared, rather than checking
      these match in number and kind.
    - This peeling is done with peel_typedef_pointer_or_reference_type
      which also peels any number of CV qualifiers (OK) and
      array-of ([N]) type components (not OK).
    - The function sets a state variable (was_indirect_type) to modify
      the behaviour of downstream comparisons, but this cannot be
      passed through recursive calls.

The effect of the indirect_type flag is to switch to comparisons by
name: identically named structs don't get introspected. Arguably, a
more useful behaviour for --leaf-changes-only mode would be to treat
any change to a named type as non-local, except in the context of the
definition of that type itself. This would be a more significant
change in behaviour.

	* include/abg-fwd.h (types_have_similar_structure): In both
	overloads, add an indirect_type argument, defaulting to
	false.
	* src/abg-ir.cc (reference_type_def constructor): Tabify.
	(types_have_similar_structure): In both overloads, add an
	indirect_type argument and update documentation text. In the
	type_base_sptr overload, pass indirect_type in the tail
	call. In the type_base* overload, replace was_indirect_type
	with indirect_type; peel CV qualifiers and typedefs without
	testing as the peel function does this; replace the
	indiscriminate peeling of qualifier/pointer/reference/array
	type components with code that checks the same
	pointer/reference/array type component is used on each side
	and makes recursive calls with indirect_type set to true; pass
	the indirect_type argument recursively when comparing other
	subtypes; move the typeid check earlier, document its purpose
	and remove unneccessary checks after later dynamic casts;
	remove an always-true conditional; add a TODO for comparing
	array types more accurately.
	* tests/data/Makefile.am: Add new test case files.
	* tests/data/test-abidiff-exit/test-leaf-peeling-v0.cc: New
	test case.
	* tests/data/test-abidiff-exit/test-leaf-peeling-v1.cc: Ditto.
	* tests/data/test-abidiff-exit/test-leaf-peeling-report.txt:
	Ditto.
	* tests/test-abidiff-exit.cc: Run new test case.

Signed-off-by: Giuliano Procida <gprocida@google.com>