Microoptimizations for VERIFY() and friends

Add branch hints and constify the intermediate evaluations of
left/right params in VERIFY3*().

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Adam Moss <c@yotes.com>
Closes #11708