linked-list test: Add test for SIGNAL_SAFE_LIST. (It currently fails.) * tests/test-asyncsafe-linked_list.sh: New file. * tests/test-asyncsafe-linked_list.c: New file. * modules/linked-list-tests (Files): Add them. (Depends-on): Add thread, yield, nanosleep, sigaction, sigprocmask. (Makefile.am): Arrange to compile test-asyncsafe-linked_list.c and run test-asyncsafe-linked_list.sh.