Replace some symbol accessor macros with functions.

gdb/ChangeLog:

	* symtab.h (SYMBOL_SYMTAB): Delete
	(SYMBOL_OBJFILE): Delete.
	(symbol_symtab, symbol_set_symtab): Declare.
	(symbol_objfile, symbol_arch): Declare.
	* symtab.c (symbol_symtab): Replaces SYMBOL_SYMTAB.  All uses updated.
	All references to symbol->symtab redirected through here.
	(symbol_set_symtab): New function.  All assignments to SYMBOL_SYMTAB
	redirected through here.
	(symbol_arch): New function.
	(symbol_objfile): New function.  Replaces SYMBOL_OBJFILE.
	All uses updated.
	* cp-namespace.c (cp_lookup_symbol_imports_or_template): Call
	symbol_arch.
	* findvar.c (default_read_var_value): Call symbol_arch.
	* guile/scm-frame.c (gdbscm_frame_block): Call symbol_objfile.
	* jv-lang.c (add_class_symtab_symbol): Call symbol_arch.
	* printcmd.c (address_info): Call symbol_arch.
	* tracepoint.c (scope_info): Call symbol_arch.