When enabled, coupled with ALLOW_DUMP = 1, will enable verbose and
unbuffered logging. Helpful for debugging Subzero bugs.

Bug: b/144688789
Change-Id: Ia5ae4456e4ec43dcf616f7f14cf88cd0911fe17b
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/38477
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>