rs6000.c (function_arg_boundary): Align for ABI_V4 when size is 8 bytes.

	* config/rs6000/rs6000.c (function_arg_boundary): Align for ABI_V4
	when size is 8 bytes.
	(function_arg_advance): Account for stack space used by AltiVec
	args when -mabi=altivec.  Simplify alignment calculations.  For
	ABI_V4, pass AltiVec vectors by reference when -mabi=no-altivec.
	(function_arg): Similarly.
	(function_arg_pass_by_reference): True for ABI_V4 AltiVec when
	not AltiVec ABI.
	(rs6000_va_arg): Correct fp arg test.  Adjust for AltiVec change.
	Correct alignment, and align before testing reg count.  Remove
	TREE_THIS_VOLATILE from reg.  Don't emit unused labels.
	(rs6000_complex_function_value): Check TARGET_HARD_FLOAT and
	TARGET_FPRS here..
	(rs6000_function_value): .. not here before call.

From-SVN: r81659