[GOLD] powerpc incremental-dump assertion failure

[GOLD] powerpc incremental-dump assertion failure

incremental-dump wants to instantiate Target_powerpc without options
being set up.  This patch fixes
  internal error in options, at gold/parameters.h:92

	* powerpc.cc (Target_powerpc::no_tprel_opt_): Rename from tprel_opt_.
	Init to false.
	(Target_powerpc::tprel_opt): Test parameters->options().tls_optimize().
	(Target_powerpc::set_tprel_opt): Delete.
	(Target_powerpc::set_no_tprel_opt): New function.  Update all uses
	of set_tprel_opt.