work around get_symbol_name () in sparc and ia64

work around get_symbol_name () in sparc and ia64

get_symbol_name () returns a char * in a out arg, which means we need to cast
to assign a literal to the variable passed to get_symbol_name ().  It seems
like better APIs than get_symbol_name () could be provided, but that seems like
a fair amount of work so just casting seems to be the betterthing to do for
now.

gas/ChangeLog:

2016-03-31  Trevor Saunders  <tbsaunde+binutils@tbsaunde.org>

	* config/tc-ia64.c (md_assemble): Add temporary variable to pass to
	get_symbol_name ().
	* config/tc-sparc.c (s_register): Cast a literal to char * in
	assignment.