... OpUnreachable and OpReturn.

Tests: dEQP-VK.spirv_assembly.instruction.compute.*
Tests: dEQP-VK.spirv_assembly.instruction.graphics.*
Bug: b/128527271
Change-Id: Iec9af723c72c873df8cbdea7c0027e2f7fa25e70
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/27774
Presubmit-Ready: Ben Clayton <bclayton@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>