Handle Linux kernel binaries with no __ksymtab section

Handle Linux kernel binaries with no __ksymtab section

Some Linux kernel binaries can have no __ksymtab section.  It's
possible that only have a __ksymtab_gpl section or no __ksymtab_gpl
either.  And apparently they can also have a __ksymtab* section full
of zeroes.

This patch gets the ELF/DWARF reader prepared to handle these cases.

	* src/abg-dwarf-reader.cc (find_section): Use elf_getshdrstrndx
	rather than poking at the elf header on our own.
	(read_context::find_any_ksymtab_section): Define new member
	function.
	(read_context::{get_symtab_format,
	try_reading_first_ksymtab_entry_using_pre_v4_19_format}): Use the
	new find_any_ksymtab_section rather than find_ksymtab_section.
	(read_context::get_nb_ksymtab_entries): Handle the absence of
	__ksymtab.
	(read_context::get_nb_ksymtab_gpl_entries): Handle the absence of
	__ksymtab_gpl.
	(read_context::load_kernel_symbol_table): Handle the case of zero
	ksymtab entries.
	(read_context::{maybe_adjust_address_for_exec_or_dyn,
	maybe_adjust_fn_sym_address, load_kernel_symbol_table}): Handle an
	address that is zero.

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