LLVM 11 deprecates the default boolean parameter which indicates whether
vector types are variable-length. Explicitly pass 'false'.

LLVM 11 introduces a FixedVectorType for this as well, which would help
readability, but we're still at LLVM 10.

Bug: b/165000222
Change-Id: I5404cfc8eea9553e15bfb54b2d3278bdf079612f
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/47768
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>