PR29573, addr2line doesn't display file/line for local symbols

PR29573, addr2line doesn't display file/line for local symbols

The DWARF standard is clear that DW_AT_linkage_name is optional.
Compilers may not provide the attribute on functions and variables,
even though the language mangles names.  g++ does not for local
variables and functions.  Without DW_AT_linkage_name, mangled object
file symbols can't be directly matched against the source-level
DW_AT_name in DWARF info.  One possibility is demangling the object
file symbols, but that comes with its own set of problems:
1) A demangler might not be available for the compiler/language.
2) Demangling doesn't give the source function name as stored in
   DW_AT_name.  Class and template parameters must be stripped at
   least.

So this patch takes a simpler approach.  A symbol matches DWARF info
if the DWARF address matches the symbol address, and if the symbol
name contains the DWARF name as a sub-string.  Very likely the name
matching is entirely superfluous.

	PR 29573
	* dwarf.c (lookup_symbol_in_function_table): Match a symbol
	containing the DWARF source name as a substring.
	(lookup_symbol_in_variable_table): Likewise.
	(_bfd_dwarf2_find_nearest_line_with_alt): If stash_find_line_fast
	returns false, fall back to comp_unit_find_line.