Bug 18894 - Fix representation of enumerators in abixml format

Bug 18894 - Fix representation of enumerators in abixml format

It turns out that using a size_t to serialize an enumerator is not
enough to represent things like enum foo {value = -3}; We need to
represent it using ssize_t.

Also, the patch avoids early canonicalization (when reading DWARF) of
types that refer to themselves.  This was leading to type degradation
(serializing the type from IR to abixml and de-serializing it back to
IR leads to a different type).

	* include/abg-ir.h (enum_type_decl::enumerator::get_value()):
	Change the type of this from size_t to ssize_t.
	* src/abg-ir.cc (enum_type_decl::enumerator::get_value): Do the
	same on the definition side.
	(non_canonicalized_subtype_detector::visit_begin): If a type
	refers to itself, late canonicalize it to have a similar hashing
	result as what the abixml reader does.
	* src/abg-reader.cc (build_enum_type_decl): Use ssize_t to read
	the value of enumerators.
	* tests/data/test-read-dwarf/test13-pr18894.so.abi: New test input.
	* tests/data/Makefile.am: Add the new test inputs above to source
	distribution.
	* tests/test-read-dwarf.cc (in_out_specs): Add new test inputs.
	* tests/data/test-read-dwarf/test9-pr18818-clang.so.abi: Adjust.
	* tests/data/test-read-dwarf/test10-pr18818-gcc.so.abi: Likewise.
	* tests/data/test-read-dwarf/test11-pr18828.so.abi: Likewise.
	* tests/data/test-read-dwarf/test12-pr18844.so.abi: Likewise.

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