use intel intrinsics xml data

[seanjensengrey]

see, rust-lang/rfcs#1639 (comment)

[eefriedman]

Hmm... I'll probably use that to generate function signatures for the rest of the intrinsics. (I did the signatures so far by copy-pasting from the Intel webpage, and using regular expressions to fix up the result.) I don't think I can use if for anything else, though.

[seanjensengrey]

It looks like the clang tests could be parsed to map between llvm intrinsics and intel intrinsics

__m128i test_mm_lddqu_si128(__m128i const* P) {
  // CHECK-LABEL: test_mm_lddqu_si128
  // CHECK: call <16 x i8> @llvm.x86.sse3.ldu.dq(i8* %{{.*}})
  return _mm_lddqu_si128(P);
}