* ggc.h (ggc_test_and_set_mark): New macro.
	(ggc_mark_rtx): Use ggc_test_and_set_mark.
	(ggc_mark_tree): Likewise.
	(ggc_mark_rtvec): Likewise.
	* ggc-common.c (ggc_mark_rtx_children): Reduce recursion.

From-SVN: r30734