rs6000: Fix separate shrink-wrapping for TARGET_MULTIPLE

rs6000: Fix separate shrink-wrapping for TARGET_MULTIPLE

We cannot use {SAVE,REST}_MULTIPLE and separate shrink-wrapping together,
not without checking when actually emitting the prologue/epilogue that the
registers to save/restore are actually still one contiguous block up to
(and including) 31.  So either:

1) We delay the decision of whether to use lmw/stmw to later;
2) We disallow shrink-wrapping separate (integer) components when those
strategies are selected; or
3) We don't use those strategies if we use separate shrink-wrapping.

This patch does 3).  In the long term it may be best to do 1) instead,
it can be slightly more efficient.

This caused problems on darwin (it is the only config that uses lmw/stmw
instructions by default).

	* config/rs6000/rs6000.c (rs6000_savres_strategy): Do not select
	{SAVE,REST}_MULTIPLE if shrink-wrapping separate components.
	(rs6000_get_separate_components): Assert we do not have those
	strategies selected.

From-SVN: r241297