[Darwin, PPC, Mode Iterators 3/n] Update macho_correct_pic.

Drop the expander and use a mode expander on the define_insn
for macho_correct_pic instead.

gcc/ChangeLog:

2019-09-27  Iain Sandoe  <iain@sandoe.co.uk>

	* config/rs6000/darwin.md (@macho_correct_pic_<mode>): New,
	replaces the expander and two define_insn entries.
	(@reload_macho_picbase_<mode>): Update gen_macho_correct_pic
	call.
	* config/rs6000/rs6000.md (builtin_setjmp_receiver): Likewise.

From-SVN: r276196