x86: Get the widest vector mode from STORE_MAX_PIECES for memset

x86: Get the widest vector mode from STORE_MAX_PIECES for memset

commit 050b1708ea532ea4840e97d85fad4ca63d4cd631
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Thu Jun 19 05:03:48 2025 +0800

    x86: Get the widest vector mode from MOVE_MAX

gets the widest vector mode from MOVE_MAX.  But for memset, it should
use STORE_MAX_PIECES.

gcc/

	PR target/121410
	* config/i386/i386-expand.cc (ix86_expand_set_or_cpymem): Use
	STORE_MAX_PIECES to get the widest vector mode in vector loop
	for memset.

gcc/testsuite/

	PR target/121410
	* gcc.target/i386/pr121410.c: New test.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>