Merge branch 'lsfd--monitor-flag-for-poll-syscall' of https://github.com/masatake...

* 'lsfd--monitor-flag-for-poll-syscall' of https://github.com/masatake/util-linux:
  tests: (test_mkfds::mkfds-multiplexing) make the output of ts_skip_subtest visible
  tests: (test_mkfds::mkfds-multiplexing) dump /proc/$pid/syscall for debugging
  lsfd: (man) write about XMODE.m and classical system calls for multiplexing
  tests: (lsfd) add a case testing XMODE.m for classical syscalls for multiplexing
  tests: (test_mkfds) add ppoll multiplexer
  tests: (test_mkfds) add poll multiplexer
  tests: (test_mkfds) add pselect6 and select multiplexers
  tests: (test_mkfds) add a new factory "multiplexing"
  tests: (test_mkfds) allow to add factory-made fds to the multiplexer as event source
  tests: (test_mkfds, refactor) make the function for waiting events plugable
  tests: (test_mkfds) include locale headers first to define _GNU_SOURCE
  tests: (test_mkfds) use err() when a system call fails
  lsfd: (comment) fix a typo
  lsfd: mark XMODE.m on fds monitored by select(2) and pselect6(2)
  lsfd: mark XMODE.m on fds monitored by poll(2) and ppoll(2)
  lsfd: cache the result of checking whether "XMODE" column is enabled or not
  procfs: add a helper function to access /proc/$pid/syscall
  lsfd: (refactor) make the code for traversing threads reusable

diff --cc meson.build
Simple merge

diff --cc tests/helpers/Makemodule.am
Simple merge