openat tests: EBADF tests. * tests/test-fchownat.c (main): Add tests for EBADF. * tests/test-fstatat.c (main): Likewise. * tests/test-mkdirat.c (main): Likewise. * tests/test-openat.c (main): Likewise. * tests/test-unlinkat.c (main): Likewise. * tests/test-fchmodat.c: New file. * modules/openat-tests (Files): Add tests/test-fchmodat.c. (Makefile.am): Also run 'test-fchmodat'.