use auto_bitmap more with alternate obstacks

use auto_bitmap more with alternate obstacks

gcc/ChangeLog:

2017-05-13  Trevor Saunders  <tbsaunde+gcc@tbsaunde.org>

	* df-core.c (df_set_blocks): Start using auto_bitmap.
	(df_compact_blocks): Likewise.
	* df-problems.c (df_rd_confluence_n): Likewise.
	* df-scan.c (df_insn_rescan_all): Likewise.
	(df_process_deferred_rescans): Likewise.
	(df_update_entry_block_defs): Likewise.
	(df_update_exit_block_uses): Likewise.
	(df_entry_block_bitmap_verify): Likewise.
	(df_exit_block_bitmap_verify): Likewise.
	(df_scan_verify): Likewise.
	* lra-constraints.c (lra_constraints): Likewise.
	(undo_optional_reloads): Likewise.
	(lra_undo_inheritance): Likewise.
	* lra-remat.c (calculate_gen_cands): Likewise.
	(do_remat): Likewise.
	* lra-spills.c (assign_spill_hard_regs): Likewise.
	(spill_pseudos): Likewise.
	* tree-ssa-pre.c (bitmap_set_and): Likewise.
	(bitmap_set_subtract_values): Likewise.

From-SVN: r248023