Opt_0 and Opt_1 are not implemented, so they weren't useful. With this
change, we can at least run Subzero's "0-1" optimization level to
compare against "02".

Bug: b/144688789
Change-Id: Ic6a5af572ed9a543f76bbc7074f87771f8da1980
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/38476Tested-by: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>