Bug 24431 Treat __ksymtab as int32_t for v4.19+ kernels

Bug 24431 Treat __ksymtab as int32_t for v4.19+ kernels

Calculating the relocation for values in __ksymtab with GElf_Addr (i.e.
uint64_t), makes the calculation rely on overflows for negative offsets.
Address that by treating these as 32bit signed values for the v4.19+
__ksymtabs and calculate the offset with them. This also allows, similar
an earlier commit, to drop the distinction between 64bit and 32bit
kernels.

	* src/abg-dwarf-reader.cc (maybe_adjust_sym_address_from_v4_19_ksymtab):
	treat passed addr as 32bit signed offset in case of v4.19+ __ksymtabs

Signed-off-by: Matthias Maennich <maennich@google.com>