InnoDB: Win64 portability fix: add missing declaration and
correct the definition of srv_max_buf_pool_modified_pct.
innobase/include/srv0srv.h:
Declare srv_max_buf_pool_modified_pct
innobase/srv/srv0srv.c:
Define srv_max_buf_pool_modified_pct as ulong,
as it is declared in ha_innodb.h.