i386: Check AX input in any_mul_highpart peepholes

When applying peephole optimization to transform

	mov imm, %reg0
	mov %reg1, %AX_REG
	imul %reg0

to

	mov imm, %AX_REG
	imul %reg1

disable peephole optimization if reg1 == AX_REG.

gcc/

	PR target/103785
	* config/i386/i386.md: Swap operand order in comments and check
	AX input in any_mul_highpart peepholes.

gcc/testsuite/

	PR target/103785
	* gcc.target/i386/pr103785.c: New test.