srv_print_thread_releases, srv_print_lock_waits, srv_print_buf_io,
srv_print_log_io, srv_print_latch_waits: Define these variables as
constants (FALSE), unless UNIV_DEBUG is defined.  These variables
are never assigned to, and they are initialized to FALSE.  It could
be useful to set them when debugging InnoDB.

srv_slot_t: Fuse the fields type, in_use, suspended to a single machine word.

srv_meter[], srv_meter_low_water[], srv_meter_high_water[],
srv_meter_high_water2[], srv_meter_foreground[]: Enclose these arrays
inside #if 0.  The arrays are essentially constants that do not affect
the control flow.

enum srv_thread_type: New enum, to replace the #defines SRV_COM, ...
Enclose the unused values SRV_BUFFER, SRV_RECOVERY, SRV_INSERT
inside #if 0, so that some arrays and loops can be reduced.