c-family: Remove names of unused parameters

c-family: Remove names of unused parameters

C++ allows unnamed parameters, which means we don't need to call them
'dummy' and mark them with the unused attribute.

gcc/c-family/ChangeLog:

	* c-pragma.cc (handle_pragma_pack): Remove parameter name.
	(handle_pragma_weak): Likewise.
	(handle_pragma_scalar_storage_order): Likewise.
	(handle_pragma_redefine_extname): Likewise.
	(handle_pragma_visibility): Likewise.
	(handle_pragma_diagnostic): Likewise.
	(handle_pragma_target): Likewise.
	(handle_pragma_optimize): Likewise.
	(handle_pragma_push_options): Likewise.
	(handle_pragma_pop_options): Likewise.
	(handle_pragma_reset_options): Likewise.
	(handle_pragma_message): Likewise.
	(handle_pragma_float_const_decimal64): Likewise.