Convert symbol_cache to type-safe registry API
This changes the symbol_cache to use the type-safe registry API.
gdb/ChangeLog
2019-05-08 Tom Tromey <tom@tromey.com>
* symtab.c (struct symbol_cache): Add destructor and
initializers.
(symbol_cache_key): Move. Change type.
(make_symbol_cache, free_symbol_cache): Remove.
(get_symbol_cache): Update.
(symbol_cache_cleanup): Remove.
(ALL_PSPACES, symbol_cache_flush)
(maintenance_print_symbol_cache)
(maintenance_print_symbol_cache_statistics, _initialize_symtab):
Update.