Rework symbol searches to move Ada-specific stuff to ada-lang.c.

Rework symbol searches to move Ada-specific stuff to ada-lang.c.

This is a clean-up of some of our symbol-lookup machinery to pull some
kludgy Ada-specific definitions out of psymtab.c.  In place of
map_ada_symtabs and ada_lookup_partial_symbol, we have a method
map_matching_symbols, which searches through all symbol tables and
partial symbol tables looking for a symbol that matches according to
a matching function that is passed as a parameter. This requires some
care, because partial symbol tables speed up searches by binary search,
while full symbol tables use hashing. To call map_matching_symbols, therefore,
you may need to supply both a matching function that is compatible with the
dictionary hash function and an ordering relation that is compatible with
strcmp_iw, which is used to order partial symbol tables.

Having added this general routine to psymtab.c, we use it in ada-lang.c
to rework add_non_local_symbols (now renamed add_nonlocal_symbols).

Changelog:

    gdb/

    * ada-lang.c (full_match): Declare.
    (ada_match_name): Rename to match_name (we should avoid prefixing static
    symbols with "ada_").
    (match_name): New name for ada_match_name.
    (struct ada_psym_data): Remove and replace with...
    (struct match_data): User data for map_matching_symbols.
    (ada_add_psyms): Remove.
    (aux_add_nonlocal_symbols): New function, used as callback for
    map_matching_symbols.
    (compare_names): Ordering function adopted from strcmp_iw for Ada-encoded
    symbols.
    (ada_add_non_local_symbols): Rename to add_nonlocal_symbols.
    (add_nonlocal_symbols): Renamed from ada_add_non_local_symbols.
    Rework to use map_matching_symbols instead of map_ada_symtabs.
    (ada_lookup_symbol_list): Use add_nonlocal_symbols.
    * psymtab.c: Include dependency on dictionary.h.
    (match_partial_symbol): New function.
    (ada_lookup_partial_symbol): Remove.
    (map_block): New function, auxiliary to map_matching_symbols_psymtab.
    (map_matching_symbols_psymtab): New function.
    (psym_functions): Replace map_ada_symtabs with map_matching_symbols_psymtab.
    * symfile.h: Replace map_ada_symtabs definition with map_matching_symbols.