Verification can take upwards of 10% of a dEQP test's execution time.

Verification is enabled for Kokoro builds and unit tests as silently regressing would be a Bad Thing.

Verification is also enabled for debug (!NDEBUG) builds.

Bug: b/135609394
Change-Id: I6c354c40f524e1e8f3e08f24129b7e008163b4bd
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/33215
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>