i386: Sync move_max/store_max with prefer-vector-width [PR112824]

i386: Sync move_max/store_max with prefer-vector-width [PR112824]

Currently move_max follows the tuning feature first, but ideally it
should sync with prefer-vector-width when it is explicitly set to keep
vector move and operation with same vector size.

gcc/ChangeLog:

	PR target/112824
	* config/i386/i386-options.cc (ix86_option_override_internal):
	Sync ix86_move_max/ix86_store_max with prefer_vector_width when
	it is explicitly set.

gcc/testsuite/ChangeLog:

	PR target/112824
	* gcc.target/i386/pieces-memset-45.c: Remove
	-mprefer-vector-width=256.
	* g++.target/i386/pr112824-1.C: New test.