Introduce rtx_expr_list subclass of rtx_def

Introduce rtx_expr_list subclass of rtx_def

gcc/
2014-08-27  David Malcolm  <dmalcolm@redhat.com>

	* coretypes.h (class rtx_expr_list): Add forward declaration.
	* emit-rtl.c (gen_rtx_EXPR_LIST): New.
	* gengenrtl.c (special_rtx): Add EXPR_LIST.
	* rtl.h (class rtx_expr_list): New subclass of rtx_def, adding
	invariant: GET_CODE (X) == EXPR_LIST.
	(is_a_helper <rtx_expr_list *>::test): New.
	(rtx_expr_list::next): New.
	(rtx_expr_list::element): New.
	(gen_rtx_EXPR_LIST): New.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@214601 138bc75d-0d04-0410-961f-82ee72b054a4