Let us try to avoid code bloat for the common case that
performance_schema is disabled at runtime, and use
ATTRIBUTE_NOINLINE member functions for instrumented latch acquisition.

Also, let us distinguish lock waits from non-contended lock requests
by using write_lock,read_lock for the requests that lead to waits,
and try_write_lock,try_read_lock for the wait-free lock acquisitions.
Actual 'try' operations are not being instrumented at all.