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

    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
76 jobs for !4713 with 2457-disable-thread-sanitizer-in-isc_dir_close in 38 minutes and 24 seconds (queued for 31 seconds)
merge request