The output registers and memory clobber were not being properly
specified, which can cause incorrect compiler transformations when these
functions are inlined cross-module via ThinLTO.

Bug: b/135066502
Change-Id: I7031d5df2d9fe0f2712e65b98cfdf5b0990db598
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/32748
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>