PR bootstrap/51872
	* hard-reg-set.h (struct hard_reg_set_container): New type.
	* target.h (struct hard_reg_set_container): Forward declare.
	* target.def (set_up_by_prologue): New target hook.
	* doc/tm.texi.in (TARGET_SET_UP_BY_PROLOGUE): Document it.
	* doc/tm.texi: Regenerated.
	* function.c (thread_prologue_and_epilogue_insns): Change
	set_up_by_prologue HARD_REG_SET into struct hard_reg_set_container.
	Call targetm.set_up_by_prologue on it.
	* config/rs6000/rs6000.c (rs6000_set_up_by_prologue): New function.
	(TARGET_SET_UP_BY_PROLOGUE): Redefine to it.

From-SVN: r183254