ThreadSanitizer: data race in __interceptor_fclose

Custom experimental snapshot of gcc version 11.0.0 20210124 on Fedora 33 (as well as GCC 10.2.1 the default Fedora 33 compiler) identified following data race in __interceptor_fclose when the rndc system test was run:

WARNING: ThreadSanitizer: data race 
  Write of size 8 at 0x000000000001 by thread T1 (mutexes: write M1, write M2):
    #0 fclose <null>
    #1 _nss_files_getprotobyname_r <null>
    #2 dns_rdata_fromtext lib/dns/rdata.c:965
    #3 load_text lib/dns/master.c:1862
    #4 dns_master_loadfile lib/dns/master.c:2703
    #5 zone_startload lib/dns/zone.c:2716
    #6 zone_load lib/dns/zone.c:2281
    #7 zone_asyncload lib/dns/zone.c:2342
    #8 dispatch lib/isc/task.c:1152
    #9 run lib/isc/task.c:1344
    #10 <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>

  Mutex M1 is already destroyed.

  Mutex M2 is already destroyed.

  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 __interceptor_fclose