Don't pass/return vectors in registers for IAMCU

Don't pass/return vectors in registers for IAMCU

Vectors should be passed in memory for IAMCU.  No warning for vector ABI
change for IAMCU since IAMCU ABI won't change.

gcc/

	PR target/66806
	* config/i386/i386.c (type_natural_mode): Don't warn vector ABI
	change for IAMCU.
	(function_arg_advance_32): Don't pass vectors in registers for
	IAMCU.
	(function_arg_32): Likewise.
	(ix86_return_in_memory): Don't return vectors in registers for
	IAMCU.

gcc/testsuite/

	PR target/66806
	* gcc.target/i386/pr66806.c: New test.

From-SVN: r225564