Use macros for some enum bit field sizes.

gdb/ChangeLog:

	* defs.h (LANGUAGE_BITS): Define.
	* psympriv.h (partial_symbol) <domain>: Use SYMBOL_DOMAIN_BITS.
	(partial_symbol) <aclass>: Use SYMBOL_ACLASS_BITS.
	* symtab.h (general_symbol_info> <language>: Usage LANGUAGE_BITS.
	(minimal_symbol_type): Add nr_minsym_types.
	(MINSYM_TYPE_BITS): Define.
	(minimal_symbol) <type>: Use MINSYM_TYPE_BITS.
	(domain_enum_tag): Add NR_DOMAINS.
	(SYMBOL_DOMAIN_BITS): Change from 4 to 3.
	(SYMBOL_ACLASS_BITS): Define from 6 to 5.