testsuite: Fix up pr123319.c [PR123319]

testsuite: Fix up pr123319.c [PR123319]

The testcase committed as gcc.dg/pr123319.c was x86_64 specific due to
immintrin.h include and use of _mm_avg_pu8 & __m64.  Furthermore, it
failed even on ia32 due to using SSE ISA stuff without -msse.

The following patch fixes that by moving that test to gcc.target/i386/,
adding -msse, adding comment with PR number, adding -msse to dg-options
and adding a new generic test written by Andrew Pinski as gcc.dg/pr123319.c.

Tested on x86_64-linux with
make check-gcc RUNTESTFLAGS='--target_board=unix\{-m32,-m32/-mno-sse,-m64\} dg.exp=pr123319.c i386.exp=pr123319.c'
both with current cc1 and cc1 from 2 days ago where everything ICEd.

2026-01-08  Jakub Jelinek  <jakub@redhat.com>
	    Andrew Pinski  <andrew.pinski@oss.qualcomm.com>

	PR tree-optimization/123319
	* gcc.dg/pr123319.c: Replace test with target independent one.  Move
	previous test to ...
	* gcc.target/i386/pr123319.c: ... here.  Add comment with PR number,
	add -msse to dg-options, move immintrin.h include right after stdint.h
	include.