LLVM 11 removes support for llvm::ConstantVector::getSplat() to take an
integer number of vector elements obtained from the getNumElements()
method. Use the new getElementCount() approach instead.

See https://reviews.llvm.org/D74386

Bug: b/188819735
Bug: b/165000222
Bug: b/178600922
Change-Id: I202a8725e1e00f35d7f5d5ee76f5538243d157b9
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/52268
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>