Consolidate ABI warning into type_natural_mode

gcc/

	PR target/59794
	* config/i386/i386.c (type_natural_mode): Add a bool parameter
	to indicate if type is used for function return value.  Warn
	ABI change if the vector mode isn't available for function
	return value.
	(ix86_function_arg_advance): Pass false to type_natural_mode.
	(ix86_function_arg): Likewise.
	(ix86_gimplify_va_arg): Likewise.
	(function_arg_32): Don't warn ABI change.
	(ix86_function_value): Pass true to type_natural_mode.
	(ix86_return_in_memory): Likewise.
	(ix86_struct_value_rtx): Removed.
	(TARGET_STRUCT_VALUE_RTX): Likewise.

gcc/testsuite/

	PR target/59794
	* g++.dg/ext/vector23.C: Also prune ABI change for Linux/x86.
	* gcc.target/i386/pr39162.c (y): New __m256i variable.
	(bar): Change return type to void.  Set y to x.
	* gcc.target/i386/pr59794-1.c: New testcase.
	* gcc.target/i386/pr59794-2.c: Likewise.
	* gcc.target/i386/pr59794-3.c: Likewise.
	* gcc.target/i386/pr59794-4.c: Likewise.
	* gcc.target/i386/pr59794-5.c: Likewise.
	* gcc.target/i386/pr59794-6.c: Likewise.
	* gcc.target/i386/pr59794-7.c: Likewise.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@206603 138bc75d-0d04-0410-961f-82ee72b054a4