Fix addr2line -i problem; reports incorrect function nesting for inline funcs.

Fix addr2line -i problem; reports incorrect function nesting for inline funcs.
* dwarf2.c (struct funcinfo): Delete nesting_level field.
(lookup_address_in_function_table): Delete code to set funcinfo
caller_func field.  Delete local curr_func.
(scan_unit_for_symbols): New locals nested_funcs, nested_funcs_size.
Delete code setting funcinfo nesting_level field.  Add code to set
funcinfo caller_func field.