Handle missing shared libraries during the examination of a core

	Handle missing shared libraries during the examination of a core
	dump gracefully.
	* solib.c (find_solib):  Use catch_errors around call to
	solib_map_sections. Use warning instead of error if reading of
	the shared library name fails.
	(solib_map_sections):  Change return and argument types to make
	it callable from catch_errors.
	(symbol_add_stub):  Avoid GDB core dump if solib->abfd is NULL.
	* irix5-nat.c, osfsolib.c (xfer_link_map_member, solib_map_sections,
	symbol_add_stub):  Ditto.