Support pandn for V1TI mode (i.e. *andnotv1ti3).

Support pandn for V1TI mode (i.e. *andnotv1ti3).

This simple patch allows the i386 backend to generate pandn instructions
for V1TI mode.  Currently, the testcase:

typedef unsigned __int128 v1ti __attribute__ ((__vector_size__ (16)));
v1ti andnot1(v1ti x, v1ti y) { return ~x & y; }

generates with -O2

        pcmpeqd %xmm2, %xmm2
        pxor    %xmm2, %xmm0
        pand    %xmm1, %xmm0
        ret

with this patch, we now generate:

        pandn   %xmm1, %xmm0
        ret

It turns out that there are currently three (near) duplicates of the
logic for andn/pandn/vandn/vpandn in i386/sse.md: one for floating point
vectors (MODEF), one for integer vectors (VI) and a third for TFmode.
Rather than introduce a fourth copy, this patch introduces a new mode
iterator to share/reuse the TFmode define_insn to also handle V1TI.

2022-04-06  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* config/i386/sse.md (ANDNOT_MODE): New mode iterator for TF and V1TI.
	(*andnottf3): Replace with...
	(*andnot<mode>3): New define_insn using ANDNOT_MODE.

gcc/testsuite/ChangeLog
	* gcc.target/i386/sse2-v1ti-andnot.c: New test case.