`SWIFTSHADER_LOGGING_LEVEL` controls how much logging we perform.
It defaults to `INFO`, so logs at `DEBUG` level are not printed by default.

Bug: b/146051794
Change-Id: I2037d1c912b24ee8d2e6543074850b65bbbd988a
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/40975Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>