get-rusage-as, pthread_sigmask tests: Fix -fsanitize=thread findings. * lib/get-rusage-as.c (get_rusage_as): When compiled by "gcc -fsanitize=thread", don't try get_rusage_as_via_setrlimit. * tests/test-pthread_sigmask2.c (main): Clean up the killer_thread before exiting.

Files:
tests/test-fseek.c
tests/test-fseek.sh
tests/test-fseek2.sh
tests/signature.h
tests/macros.h
m4/ungetc.m4

Depends-on:

configure.ac:
gl_FUNC_UNGETC_WORKS

Makefile.am:
TESTS += test-fseek.sh test-fseek2.sh
check_PROGRAMS += test-fseek