Make various gas symbol predicates and accessors take const args

Make various gas symbol predicates and accessors take const args

	* symbols.c (S_IS_FUNCTION, S_IS_EXTERNAL, S_IS_WEAK),
	(S_IS_WEAKREFR, S_IS_WEAKREFD, S_IS_COMMON, S_IS_DEFINED),
	(S_FORCE_RELOC, S_IS_DEBUG, S_IS_LOCAL, S_IS_STABD),
	(symbol_previous, symbol_next, symbol_X_add_number),
	(symbol_get_frag, symbol_used_p, symbol_used_in_reloc_p),
	(symbol_mri_common_p, symbol_written_p, symbol_removed_p),
	(symbol_resolved_p, symbol_resolving_p, symbol_section_p),
	(symbol_equated_p, symbol_equated_reloc_p, symbol_constant_p),
	(symbol_shadow_p, symbol_same_p): Constify sym args.
	* symbols.h: Update prototypes.