ia32: Disallow mode(V1TI) [PR103020]

As discussed in the PR, TImode isn't supported for -m32 on x86 (for the same
reason as on most 32-bit targets, no support for > 2 * BITS_PER_WORD
precision integers), but since PR32280 V1TImode is allowed with -msse in SSE
regs, V2TImode with -mavx or V4TImode with -mavx512f.
typedef __int128 V __attribute__((vector_size ({16,32,64}));
will not work, neither typedef int I __attribute__((mode(TI)));
but mode(V1TI), mode(V2TI) etc. are accepted with a warning when those
ISAs are enabled.  But they are certainly not fully supported, for some
optabs maybe, but most of them will not.  And, veclower lowering those ops
to TImode scalar operations will not work either because TImode isn't
supported.

So, this patch keeps V1TImode etc. in VALID*_MODE macros so that we can use
it in certain instructions, but disallows it in
targetm.vector_mode_supported_p, so that we don't offer those modes to the
user as supported.

2021-11-02  Jakub Jelinek  <jakub@redhat.com>

	PR target/103020
	* config/i386/i386.c (ix86_vector_mode_supported_p): Reject vector
	modes with TImode inner mode if 32-bit.

	* gcc.target/i386/pr103020.c: New test.