Avoid a system call when no sleep is required. Sleep in a loop (actually
two loops) to handle interruption by signals.
PR libstdc++/80538
* src/c++11/thread.cc (this_thread::__sleep_for)
[_GLIBCXX_HAVE_SLEEP]: Only call sleep for non-zero values.
Loop while sleep call is interrupted and until steady_clock
shows requested duration has elapsed.
(!_GLIBCXX_HAVE_USLEEP]: Use the _GLIBCXX_HAVE_SLEEP code path, but
avoiding the usleep call.
* testsuite/30_threads/this_thread/60421.cc: Test repeated
signal interruptions.
From-SVN: r265044
