Fix non-x86 build of LLVM Reactor
Fix non-x86 build of LLVM Reactor

LLVM 10's CreateShuffleVector() doesn't take an array of signed integers
as the shuffle mask parameter. To be compatible with both old and new
versions of LLVM, use the function which takes an array of
llvm::Constant instead.

We didn't catch this sooner because the fallback implementations of
some x86 intrinsics are not built on x86, so this change also makes
their compilation unconditional, using [[maybe_unused]] to avoid
pedantic warnings treated as errors.

Bug: b/165000222
Change-Id: Idd42eab17b65a38564ea6293daec5a4d6af8d6fe
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/62608
Reviewed-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>
Kokoro-Result: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Tested-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>

google/swiftshader,google/swiftshader,google/swiftshader