Make decl_base::get_context_rel() return a naked pointer

Make decl_base::get_context_rel() return a naked pointer

Accessing the context relationship of declarations and setting some
member properties appear to be high in performance profiles due to
shared pointer handling.  This patch makes the context relationship
accessors return a naked pointer and also passes a bunch of shared
pointer as references around.

	* include/abg-fwd.h (set_member_is_static): Add an overload that
	takes the member as a reference to a smart pointer.
	(set_member_function_{is_dtor, is_ctor, is_const, vtable_offset,
	is_virtual}): Pass the member function as a reference.
	(set_member_function_is_const, set_member_function_is_virtual):
	Pass the member function as a non-const reference.
	* include/abg-ir.h (decl_base::get_context_rel): Return a naked
	pointer.
	(set_member_is_static, set_member_function_is_virtual): Adjust
	this friend declaration.
	(set_member_access_specifier): Add an overload that takes a
	reference to the member.  Pass a reference to smart pointer to the
	other overload.
	(set_member_function_is_{is_ctor,is_dtor,is_const,is_virtual,vtable_offset}):
	Take a non-const reference to function_decl.
	* src/abg-ir.cc (decl_base::get_context_rel): Likewise.
	(equals(const decl_base&, const decl_base&, change_kind*)):
	Adjust.
	(equals(const var_decl&, const var_decl&, change_kind*)):
	Likewise.
	(get_member_access_specifier, get_member_is_static)
	(set_data_member_offset, get_data_member_offset)
	(set_data_member_is_laid_out, get_data_member_is_laid_out)
	(get_member_function_is_ctor, set_member_function_is_ctor)
	(get_member_function_is_dtor, set_member_function_is_dtor)
	(get_member_function_is_const, set_member_function_is_const)
	(get_member_function_vtable_offset)
	(set_member_function_vtable_offset)
	(get_member_function_is_virtual, set_member_function_is_virtual):
	Likewise.
	(set_member_access_specifier): Add an overload that takes a
	reference to decl_base.
	(set_member_is_static, set_member_function_{is_dtor, is_ctor,
	is_const, vtable_offset, is_virtual}): Pass the member function as
	a reference.): Add an overload that takes the member as a
	reference, and write the older overload in terms of the new one.

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