Support suppressing data member insertion before a flexible array member

Support suppressing data member insertion before a flexible array member

Consider this code example:

    $ cat test-v0.c
     1	struct foo
     2	{
     3	  int member0;
     4	  char pad[]; /* <-- flexible array member.  */
     5	};
     6
     7	void
     8	foo(struct foo * p __attribute__((unused)))
     9	{
    10	}
    $

Consider this new version of the code where a data member has been
added right before the flexible array member:

    $ cat -n test-v1.c
     1	struct foo
     2	{
     3	  int member0;
     4	  char member1; /*<-- added member.  */
     5	  char pad[]; /* <-- flexible array member.  */
     6	};
     7
     8	void
     9	foo(struct foo * p __attribute__((unused)))
    10	{
    11	}
    $

Here is what abidiff reports about the change:

    $ abidiff test-v0.o test-v1.o || echo "returned value: $?"
    Functions changes summary: 0 Removed, 1 Changed, 0 Added function
    Variables changes summary: 0 Removed, 0 Changed, 0 Added variable

    1 function with some indirect sub-type change:

      [C] 'function void foo(foo*)' at test-v0.c:8:1 has some indirect sub-type changes:
	parameter 1 of type 'foo*' has sub-type changes:
	  in pointed to type 'struct foo' at test-v1.c:1:1:
	    type size changed from 32 to 64 (in bits)
	    1 data member insertion:
	      'char member1', at offset 32 (in bits) at test-v1.c:4:1
	    1 data member change:
	      'char pad[]' offset changed from 32 to 40 (in bits) (by +8 bits)

    returned value: 4
    $

This patch allows users to suppress this change report using a new
property value to the "has_data_member_inserted_at" property of the
[suppress_type] directive.  The resulting suppression specification
reads:

    $ cat -n foo.suppr
	 1	[suppress_type]
	 2	 type_kind = struct
         3       name = foo
	 4	 has_data_member_inserted_at = offset_of_flexible_array_data_member
	 5	 has_size_change = yes
    $

With this suppression specification the previous command now gives:

    $ abidiff --suppr foo.suppr test-v0.o test-v1.o && echo "returned value: $?"
    Functions changes summary: 0 Removed, 0 Changed (1 filtered out), 0 Added function
    Variables changes summary: 0 Removed, 0 Changed, 0 Added variable

    returned value: 0
    $

The patch adds new test cases and updates the documentation to add a
mention to the new offset_of_flexible_array_data_member named
boundary.

	* doc/manuals/libabigail-concepts.rst: Add documentation for the
	new "offset_of_flexible_array_data_member" named boundary.
	* include/abg-fwd.h (has_flexible_array_data_member): Declare new
	function.
	* src/abg-ir.cc (has_flexible_array_data_member): Define it.
	* include/abg-suppression.h
	(type_suppression::insertion_range::named_boundary_sptr): Define
	new typedef.
	(type_suppression::insertion_range::create_named_boundary): Declare
	new static function member function.
	(is_named_boundary): Declare new function.
	(class type_suppression::insertion_range::named_boundary): Declare
	new type.
	* src/abg-suppression.cc
	(struct type_suppression::insertion_range::named_boundary::priv):
	Define new private type.
	(OFFSET_OF_FLEXIBLE_ARRAY_DATA_MEMBER_STRING): Define new static
	constant string getter function.
	(type_suppression::insertion_range::create_named_boundary): Define
	new static member function.
	(is_named_boundary): Define new function.
	(read_type_suppression): Parse the new
	"offset_of_flexible_array_data_member" named boundary.
	(type_suppression::insertion_range::eval_boundary): Evaluate the
	new "offset_of_flexible_array_data_member" named boundary.
	* tests/data/test-abidiff-exit/test-fam1-report-[1-5].txt: New
	reference test output.
	* tests/data/test-abidiff-exit/test-fam2-report-1.txt: Likewise.
	* tests/data/test-abidiff-exit/test-fam1-suppr-[1-4].abignore: New test
	suppression specification.
	* tests/data/test-abidiff-exit/test-fam{1,2}-v{0,1}.o: New test input
	binaries.
	* tests/data/test-abidiff-exit/test-fam{1,2}-v{0,1}.c: Source code of
	the test input binaries.
	* tests/data/Makefile.am: Add the new test material to the source
	distribution.
	* tests/test-abidiff-exit.cc (in_out_specs): Add the new test
	input to this harness.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>