The LLVM Unreachable instruction is a terminator instruction.
It is illegal to place any instructions after this in the same block.

Bug: b/131914569
Change-Id: I6dd4ca4f8ca911dc94ba5674db598078060ef795
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/30453Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Ben Clayton <bclayton@google.com>