asan: readelf leak in hppa_process_unwind

This extracts code reading symbol tables into a common function that
tidies up after errors.  I've also changed an error reporting multiple
string tables to an error on multiple symbol tables.

	* readelf.c (get_symbols): New function.
	(process_relocs, ia64_process_unwind, hppa_process_unwind),
	(arm_process_unwind, get_symbol_for_build_attribute): Use it.