asyncsafe-linked_list failure on Fedora, Ubuntu

[Paul Eggert]

On both Ubuntu 20.10 x86-64 and Fedora 33 x86-64 the command:

./gnulib-tool --test clean-temp-simple linked-list

reports "FAIL: test-asyncsafe-linked_list.sh". This appears to be a 
combination of the two modules; if one test either individual module, 
the test works.

The created test-asyncsafe-linked_list.sh.log file says:

cat ./testdir163898/build/gltests/test-asyncsafe-linked_list.sh.log
sum = 404872, expected 436785 or 429728
../../gltests/test-asyncsafe-linked_list.sh: line 4: 191506 Aborted 
           (core dumped) ${CHECKER} 
./test-asyncsafe-linked_list${EXEEXT} $i
test-asyncsafe-linked_list.sh: test case 1 failed
sum = 338326, expected 321208 or 321208
../../gltests/test-asyncsafe-linked_list.sh: line 4: 191513 Aborted 
           (core dumped) ${CHECKER} 
./test-asyncsafe-linked_list${EXEEXT} $i
test-asyncsafe-linked_list.sh: test case 2 failed
Sent 5000 signals. Received 4874 signals. Done after 1280208 mutations.
FAIL test-asyncsafe-linked_list.sh (exit status: 1)