Disable Thread Sanitizer in isc_dir_close()

There's a false positive reported by Thread Sanitizer between the epoll_ctl() called from libuv and closedir() called from libisc. The Thread Sanitizer monitors file descriptors, but there's no possible way the file descriptor in epoll_ctl() could be the same as the directory being closed(). Let's just disable the the Thread Sanitizer for isc_dir_close() function to prevent reporting of this false positive.

Closes: #2457 (closed)

WARNING: ThreadSanitizer: data race
  Write of size 8 at 0x000000000001 by thread T1:
#0 closedir <null>
#1 isc_dir_close lib/isc/unix/dir.c:134
#2 dns_dnssec_findmatchingkeys lib/dns/dnssec.c:1526
#3 statefile_exist lib/dns/zone.c:5858
#4 dns_zone_secure_to_insecure lib/dns/zone.c:5905
#5 dns_zone_use_kasp lib/dns/zone.c:5917
#6 add_sigs lib/dns/zone.c:6901
#7 dns__zone_updatesigs lib/dns/zone.c:8225
#8 zone_nsec3chain lib/dns/zone.c:8921
#9 zone_maintenance lib/dns/zone.c:11211
#10 zone_timer lib/dns/zone.c:14674
#11 dispatch lib/isc/task.c:1152
#12 run lib/isc/task.c:1344
#13 <null> <null>

  Previous read of size 8 at 0x000000000001 by thread T2:
#0 epoll_ctl <null>
#1 uv__platform_invalidate_fd <null>
#2 uv_run <null>
#3 <null> <null>

  Location is file descriptor 143 created by thread T2 at:
#0 accept4 <null>
#1 uv__accept <null>
#2 <null> <null>

  Thread T1 (running) created by main thread at:
#0 pthread_create <null>
#1 isc_thread_create lib/isc/pthreads/thread.c:73
#2 isc_taskmgr_create lib/isc/task.c:1434
#3 create_managers bin/named/main.c:940
#4 setup bin/named/main.c:1248
#5 main bin/named/main.c:1548

  Thread T2 (running) created by main thread at:
#0 pthread_create <null>
#1 isc_thread_create lib/isc/pthreads/thread.c:73
#2 isc_nm_start lib/isc/netmgr/netmgr.c:290
#3 create_managers bin/named/main.c:934
#4 setup bin/named/main.c:1248
#5 main bin/named/main.c:1548

SUMMARY: ThreadSanitizer: data race in closedir

Closes #2457 (closed)