[X86][SSE] Recognise v2i64 comparison patterns

Bugzilla Link	33614
Version	trunk
OS	Windows NT
CC	@nikic,@rotateright

Extended Description

Before SSE41/SSE42, the only way to compare eq/gt v2i64 vectors was to use the v4i32 intrinsics:

__m128i alt_cmpeq_epi64(__m128i a, __m128i b) {
  __m128i c = _mm_cmpeq_epi32(a, b);
  return _mm_and_si128( c, _mm_shuffle_epi32( c, _MM_SHUFFLE(2,3,0,1) ) );
}

__m128i alt_cmpgt_epi64(__m128i a, __m128i b) {
  __m128i flip = _mm_setr_epi32( 0x80000000,0x00000000,0x80000000,0x00000000 );
  a = _mm_xor_si128( a, flip );
  b = _mm_xor_si128( b, flip );
  __m128i gt = _mm_cmpgt_epi32( a, b );
  __m128i gt0 = _mm_shuffle_epi32( gt, _MM_SHUFFLE(2,2,0,0) );
  __m128i gt1 = _mm_shuffle_epi32( gt, _MM_SHUFFLE(3,3,1,1) );
  __m128i eq = _mm_cmpeq_epi32( a, b );
  __m128i eq0 = _mm_shuffle_epi32( eq, _MM_SHUFFLE(3,3,1,1) );
  return _mm_or_si128( _mm_and_si128( gt0, eq0 ), gt1 );
}


__m128i alt_cmpgt_epu64(__m128i a, __m128i b) {
  __m128i flip = _mm_set1_epi32( 0x80000000 );
  a = _mm_xor_si128( a, flip );
  b = _mm_xor_si128( b, flip );
  __m128i gt = _mm_cmpgt_epi32( a, b );
  __m128i gt0 = _mm_shuffle_epi32( gt, _MM_SHUFFLE(2,2,0,0) );
  __m128i gt1 = _mm_shuffle_epi32( gt, _MM_SHUFFLE(3,3,1,1) );
  __m128i eq = _mm_cmpeq_epi32( a, b );
  __m128i eq0 = _mm_shuffle_epi32( eq, _MM_SHUFFLE(3,3,1,1) );
  return _mm_or_si128( _mm_and_si128( gt0, eq0 ), gt1 );
}

Resulting in quite a bit of legacy code that still uses this (I've only seen this in __m128i code). We should be trying to simplify this where possible.