[Darwin, PPC, Mode Iterators 2/n] Eliminate picbase expanders.

[Darwin, PPC, Mode Iterators 2/n] Eliminate picbase expanders.

We can use the mode iterators directly with an @pattern to avoid the
need for an expander that was only there to pass the mode through.

gcc/ChangeLog:

2019-09-26  Iain Sandoe  <iain@sandoe.co.uk>

	* config/rs6000/darwin.md: Replace the expanders for
	load_macho_picbase and reload_macho_picbase with use of '@'
	in their respective define_insns.
	(nonlocal_goto_receiver): Pass Pmode to gen_reload_macho_picbase.
	* config/rs6000/rs6000-logue.c (rs6000_emit_prologue): Pass
	Pmode to gen_load_macho_picbase.
	* config/rs6000/rs6000.md: Likewise.

From-SVN: r276159