Tweak interface to ira-build.c:ior_hard_reg_conflicts

This patch makes ior_hard_reg_conflicts take a const_hard_reg_set
rather than a pointer, so that it can be passed a temporary object
in later patches.

2019-09-09  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* ira-int.h (ior_hard_reg_conflicts): Take a const_hard_reg_set
	instead of a HARD_REG_SET *.
	* ira-build.c (ior_hard_reg_conflicts): Likewise.
	(ira_build): Update call accordingly.
	* ira-emit.c (add_range_and_copies_from_move_list): Likewise.

From-SVN: r275535