If enabled, and ALLOW_DUMP = 1, emit() outputs text asm to stdout along
with liveness info. Useful for debugging register allocation.

Bug: b/144688789
Change-Id: I36137c439f6f2ca32af6f208146501b095ccfac4
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/38478Tested-by: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>