Implement a poor-man's RTTI for performance

Implement a poor-man's RTTI for performance

Profiling showed that a number of use of dynamic_cast are a speed
bottleneck.

This patch implements a poor-man's RTTI that allows us to implement a
form of dynamic_cast that is specific to the types of the internal
reprenstation that are in the namespace abigail::ir.  It speeds up
things greatly.

Basically, the base type of all ABI artifacts
(abigail::ir::type_or_decl_base) now contains three new data members.
The first one contains a bitmap that identifies the type of artifact.
The second one contains a pointer to the dynamic type sub-object of
the current instance of the artifact.  The last one contains either a
pointer to the type_base sub-object of the current instance of ABI
artifact if it's a type, or a pointer to the type_decl sub-object of
the current instance.

Together these three data members allow the patch to implement the
abigail::ir::{is_type(), is_decl(), is_<type_kind>_type} functions
that we need to make the code base noticeably faster when using abidw
on a big vmlinux binary.

	* include/abg-fwd.h (is_type_decl): Replace the overloads
	that takes a type_base* and/or a decl_base* by one that takes a
	type_or_decl_base*.
	* include/abg-ir.h (type_or_decl_base::type_or_decl_kind): Define
	new enum.
	(type_or_decl_base::{kind, runtime_type_instance,
	type_or_decl_base_pointer}): Declare new accessors.
	(operator{|,|=,&,&=): Declare new operators for the new
	type_or_decl_base::type_or_decl_kind enum.
	(global_scope::global_scope): Move the definition of this
	constructor to ...
	* src/abg-ir.cc (global_scope::global_scope): ... here.
	(type_or_decl_base::priv::{kind_, rtti_, type_or_decl_ptr_}):
	Add new data members.
	(type_or_decl_base::priv::priv): Take a
	type_or_decl_base::type_or_decl_kind enum.
	(type_or_decl_base::priv::kind): Define new accessors.
	(operator{|,|=,&,&=): Define new operators for the new
	type_or_decl_base::type_or_decl_kind enum.
	(type_or_decl_base::type_or_decl_base): Take a
	type_or_decl_base::type_or_decl_kind enum.
	(type_or_decl_base::{kind, runtime_type_instance,
	type_or_decl_base_pointer}): Define new accessors.
	(decl_base::decl_base, scope_decl::scope_decl)
	(type_base::type_base, scope_type_decl::scope_type_decl)
	(class_or_union::class_or_union) : Adjust to set the runtime type
	identifier of the instances of these types.
	(global_scope::global_scope, type_decl::type_decl)
	(qualified_type_def::qualified_type_def)
	(pointer_type_def::pointer_type_def)
	(reference_type_def::reference_type_def
	array_type_def::subrange_type::subrange_type)
	(array_type_def::array_type_def, enum_type_decl::enum_type_decl)
	(typedef_decl::typedef_decl, var_decl::var_decl)
	(function_type::function_type, method_type::method_type)
	(function_decl::function_decl)
	(function_decl::parameter::parameter, method_decl::method_decl)
	(class_decl::class_decl, class_decl::base_spec::base_spec)
	(union_decl::union_decl, template_decl::template_decl)
	(type_tparameter::type_tparameter)
	(non_type_tparameter::non_type_tparameter)
	(template_tparameter::template_tparameter)
	(type_composition::type_composition)
	(function_tdecl::function_tdecl, function_tdecl::function_tdecl)
	(class_tdecl::class_tdecl):
	Likewise and call runtime_type_instance() here to set the runtime
	type instance pointers of the current instance.
	(is_decl, is_type, is_class_type, is_pointer_type): Adjust to use
	the new poor-man's rtti machinery.
	(is_type_decl): Replace the overloads that takes a type_base*
	and/or a decl_base* by one that takes a type_or_decl_base*.
	(pointer_type_def::operator==, class_decl::operator==): Use the
	poor-man's rtti machinery to replace dynamic_cast.
	hash_type_or_decl: Replace dynamic_cast<const type_base> by
	is_type() and dynamic_cast<const decl_base*> by is_decl().

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