Implement de-duplication for types and decls at DWARF loading time
    
    Many types and decls are redefined in every translation unit that make
    up an ELF binary.  This patch detects that a DIE represents a type or
    decl that has already been defined in the current corpus and so will
    not create a new internal representation for it.
    
    The patch defines facilities to build the pretty representation of a
    type or decl.  It's by looking at the pretty representation of a DIE
    that the patch detects that a different DIE has already defined the
    same type or decl.
    
    The patch also fixes detection of the const-ness of member functions
    as there were many cases where const member functions were not
    recognized as const.  This fix makes it so that the pretty
    representation of the DIE of said member functions match the pretty
    representation of their internal representation, as far as the
    const-ness is concerned.
    
    One bit of infrastructure change that is used by the const-ness fix is
    that method_type now carries const-ness.  So a method_decl that has a
    const method_type is going to be const itself.
    
    	* include/abg-ir.h (method_type::priv_): Introduce new pimpl
    	pointer here.
    	(method_type::class_type_): Move this into the pimpl idiom.
    	(method_type::method_type): Take a new is_const flag.
    	(method_type::get_class_type): Make this method out-of-line.
    	(method_type::{s,g}et_is_const): Declare new member functions.
    	(get_method_type_name): Declare this function as a friend of
    	the method_type type.
    	* src/abg-dwarf-reader.cc: Include the new abg-ir-priv.h and
    	abg-corpus-priv.h.
    	(typedef die_tu_map_type): Fix comment.
    	(typedef die_istring_map_type): New typedef.
    	(class read_context::die_source_dependant_container_set): New
    	class template.
    	(read_context::{die_qualified_name_maps_, die_pretty_repr_maps_,
    	die_pretty_type_repr_maps_}): Define new data members.
    	(read_context::{get_die_qualified_name, get_die_qualified_name,
    	get_die_qualified_type_name, get_die_pretty_type_representation,
    	get_die_pretty_representation, lookup_type_artifact_from_die,
    	lookup_artifact_from_die, lookup_artifact_from_die_representation,
    	associate_die_to_artifact_by_repr,
    	associate_die_to_artifact_by_repr_internal,
    	lookup_type_from_die}): Define new member functions.
    	(read_context::lookup_type_from_die_offset): Fix comment.
    	(get_parent_die, get_scope_die, die_is_decl)
    	(die_is_namespace, die_is_unspecified, die_is_void_type)
    	(die_is_pointer_type, die_is_reference_type)
    	(die_is_pointer_or_reference_type, die_is_class_type)
    	(die_has_object_pointer, die_this_pointer_from_object_pointer)
    	(die_this_pointer_is_const, is_decl_tag)
    	(die_object_pointer_is_for_const_method, die_is_at_class_scope)
    	(die_name, die_qualified_type_name, die_qualified_decl_name)
    	(die_qualified_name, die_qualified_type_name_empty)
    	(die_return_and_parm_names_from_fn_type_die)
    	(die_function_signature, die_peel_qual_ptr)
    	(die_function_type_is_method_type, die_pretty_print_type)
    	(die_pretty_print_decl, die_pretty_print)
    	(build_subranges_from_array_type_die)
    	(build_or_get_fn_decl_if_not_suppressed)
    	(lookup_class_or_typedef_type)
    	(lookup_class_typedef_or_enum_type_from_corpus)
    	(is_function_for_die_a_member_of_class)
    	(add_or_update_member_function): Define new static functions.
    	(read_context::associate_die_to_decl): Call
    	associate_die_to_artifact_by_repr.
    	(read_context::{associate_die_to_type,
    	schedule_type_for_late_canonicalization}): Take just one "die"
    	parameter rather than taking a die offset and a die source; adjust
    	accordingly.
    	(maybe_canonicalize_type): Likewise.
    	(finish_member_function_reading): Take a const reference to
    	function_decl_sptr.
    	(die_loc_and_name): Use the new die_name function.
    	(die_is_type): Rename is_type_die into this.
    	(build_type_decl): Take a new "where_offset" parameter.  Adjust.
    	If a type of the same name as the one for the current DIE is is
    	already present, do not create a new type; just return the
    	already-existing one.
    	(build_enum_type): Take a new "where_offset" parameter.  Adjust.
    	(finish_member_function_reading): Pass two smart pointers by const
    	reference.  Assert that the type of the member function is a
    	method_type.  Some light cleanups.
    	(add_or_update_class_type): Rename build_class_type_and_add_to_ir.
    	If a DIE defining the same class has already been seen, then
    	return that class; don't construct any other internal
    	representation for the same class.  Better handle the updating of
    	member data and functions.  Do not duplicate member types.
    	(build_qualified_type, build_pointer_type_def)
    	(build_reference_type): Support de-duplication here.
    	(build_function_type): Likewise.  Support detection and building
    	of method type.  This also supports *const* method type building.
    	(build_array_type): Use the new
    	build_subranges_from_array_type_die.
    	(build_type_decl): Cleanup logic.
    	(build_or_get_var_decl_if_not_suppressed): Renamed
    	build_var_decl_if_not_suppressed into this.  Perform
    	de-duplication for data members.
    	(build_function_decl): Don't set an empty source location.  If the
    	function type cannot be constructed, do not construct the function
    	decl either.  Adjust.
    	(build_ir_node_from_die): Adjust.  When building a function for a
    	DW_TAG_subroutine_type DIE, use the new
    	build_or_get_fn_decl_if_not_suppressed.
    	* src/abg-ir.cc (translation_unit::bind_function_type_life_time):
    	Fix comment.
    	(strip_typedef): Adjust.
    	(qualified_type_def::build_name): Set the prefix name of a the
    	name of a noop qualifier to "noop-qual", just like what is done in
    	the new die_qualified_name function.
    	(struct method_type::priv): New priv type for the method_type
    	class.
    	(method_type::method_type): Take a new 'is_const' parameter.
    	Adjust as the method_type is now pimpl'ed.
    	(method_type::{get_class_type, set_is_const, get_is_const}):
    	Define new member functions.
    	(function_decl::get_pretty_representation_of_declarator): Better
    	detecter of const-ness.
    	(class_decl::insert_member_decl):  Better setting of the
    	const-ness.
    	(class_decl::method_decl::method_decl): Adjust.  Deduce the
    	const-ness of the method_decl from the const-ness of its
    	method_type.
    	(copy_member_function): Adjust.
    	(set_member_is_static): Do not assume a non-nil scope anymore
    	because member_decl can now be scope-less, at least for a little
    	while.
    	* src/abg-reader.cc (push_decl_to_current_scope): Adjust.
    	(build_function_decl): Style adjustment.  Adjust for method_type
    	const-ness changes.
    	(build_function_type): Likewise.  Also, support the new
    	"method-class-id" property that flags a function type as being a
    	method type.
    	* src/abg-writer.cc (write_function_decl): Style fixes.
    	(write_function_type): Likewise.  Emit a new "method-class-id"
    	property for function type that is actually a method type.  That
    	property's value is the id of the class of the method type.
    	* tests/data/test-diff-dwarf-abixml/test0-pr19026-libvtkIOSQL-6.1.so.1.abi: Adjust.
    	* tests/data/test-diff-dwarf/test0-report.txt: Adjust.
    	* tests/data/test-diff-filter/test0-report.txt: Adjust.
    	* tests/data/test-diff-filter/test01-report.txt: Adjust.
    	* tests/data/test-diff-filter/test30-pr18904-rvalueref-report0.txt: Adjust.
    	* tests/data/test-diff-filter/test30-pr18904-rvalueref-report1.txt: Adjust.
    	* tests/data/test-diff-filter/test31-pr18535-libstdc++-report-0.txt: Adjust.
    	* tests/data/test-diff-filter/test31-pr18535-libstdc++-report-1.txt: Adjust.
    	* tests/data/test-diff-pkg/libICE-1.0.6-1.el6.x86_64.rpm--libICE-1.0.9-2.el7.x86_64.rpm-report-0.txt: Adjust.
    	* tests/data/test-diff-pkg/libsigc++-2.0-0c2a_2.4.0-1_amd64--libsigc++-2.0-0v5_2.4.1-1ubuntu2_amd64-report-0.txt: Adjust.
    	* tests/data/test-diff-pkg/tbb-4.1-9.20130314.fc22.x86_64--tbb-4.3-3.20141204.fc23.x86_64-report-0.txt: Adjust.
    	* tests/data/test-diff-pkg/tbb-4.1-9.20130314.fc22.x86_64--tbb-4.3-3.20141204.fc23.x86_64-report-1.txt: Adjust.
    	* tests/data/test-read-dwarf/libtest23.so.abi: Adjust.
    	* tests/data/test-read-dwarf/libtest24-drop-fns-2.so.abi: Adjust.
    	* tests/data/test-read-dwarf/libtest24-drop-fns.so.abi: Adjust.
    	* tests/data/test-read-dwarf/test10-pr18818-gcc.so.abi: Adjust.
    	* tests/data/test-read-dwarf/test11-pr18828.so.abi: Adjust.
    	* tests/data/test-read-dwarf/test12-pr18844.so.abi: Adjust.
    	* tests/data/test-read-dwarf/test13-pr18894.so.abi: Adjust.
    	* tests/data/test-read-dwarf/test14-pr18893.so.abi: Adjust.
    	* tests/data/test-read-dwarf/test15-pr18892.so.abi: Adjust.
    	* tests/data/test-read-dwarf/test16-pr18904.so.abi: Adjust.
    	* tests/data/test-read-dwarf/test17-pr19027.so.abi: Adjust.
    	* tests/data/test-read-dwarf/test18-pr19037-libvtkRenderingLIC-6.1.so.abi: Adjust.
    	* tests/data/test-read-dwarf/test19-pr19023-libtcmalloc_and_profiler.so.abi: Adjust.
    	* tests/data/test-read-dwarf/test20-pr19025-libvtkParallelCore-6.1.so.abi: Adjust.
    	* tests/data/test-read-dwarf/test21-pr19092.so.abi: Adjust.
    	* tests/data/test-read-dwarf/test22-pr19097-libstdc++.so.6.0.17.so.abi: Adjust.
    	* tests/data/test-read-dwarf/test8-qualified-this-pointer.so.abi: Adjust.
    	* tests/data/test-read-dwarf/test9-pr18818-clang.so.abi: Adjust.
    
    Signed-off-by: Dodji Seketeli <dodji@redhat.com>