Prevent lwlock dtrace probes from unnecessary work

Prevent lwlock dtrace probes from unnecessary work

If dtrace is compiled in but disabled, the lwlock dtrace probes still
evaluate their arguments.  Since PostgreSQL 13, T_NAME(lock) does
nontrivial work, so it should be avoided if not needed.  To fix, make
these calls conditional on the *_ENABLED() macro corresponding to each
probe.

Reviewed-by: Craig Ringer <craig.ringer@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/CAGRY4nwxKUS_RvXFW-ugrZBYxPFFM5kjwKT5O+0+Stuga5b4+Q@mail.gmail.com