rs6000: Some rs6000_emit_epilogue improvements

rs6000: Some rs6000_emit_epilogue improvements

This uses epilogue_type directly.  It also changes some ints to bools,
declares variables later, and simplifies some code.

There is one actual change:

   else if (info->push_p
           && DEFAULT_ABI != ABI_V4
-          && !crtl->calls_eh_return)
+          && epilogue_type != EPILOGUE_TYPE_EH_RETURN)
     {
       /* Prevent reordering memory accesses against stack pointer restore.  */

(different because calls_eh_return can be true for sibcalls).  This is
a bugfix.  The code was never exercised.

One place in the epilogue still uses crtl->calls_eh_return.  If that
is changed the prologue has to have a corresponding change, and the
emit_prologue function does not have an epilogue_type parameter, so
bail on changing this for now.  We might want to do this (saving the
CR fields to separate stack slots) always, not just for functions
calling eh_return, but that will require more investigation.

	* config/rs6000/rs6000.c (restore_saved_cr): Change a boolean
	argument to be type bool (was int before).
	(rs6000_emit_epilogue): Simplify some code.  Declare some variables
	at first use.  Use type bool for some variables.  Fix a theoretical
	eh_return bug for svr4.

From-SVN: r271361