PR libstdc++/71856
	* include/bits/c++config (_GLIBCXX_ASSERTIONS): Define to 1 not empty.
	* include/parallel/compiletime_settings.h (_GLIBCXX_ASSERTIONS):
	Rename to _GLIBCXX_PARALLEL_ASSERTIONS and make default value depend
	on _GLIBCXX_ASSERTIONS.
	* include/parallel/balanced_quicksort.h: Rename _GLIBCXX_ASSERTIONS.
	Include <unistd.h> for sleep.
	* include/parallel/losertree.h: Rename _GLIBCXX_ASSERTIONS.
	* include/parallel/merge.h: Likewise.
	* include/parallel/multiway_merge.h: Likewise.
	* include/parallel/partition.h: Likewise.
	* include/parallel/queue.h: Likewise.
	* include/parallel/sort.h: Likewise.
	* testsuite/25_algorithms/headers/algorithm/
	parallel_algorithm_assert.cc: New.

From-SVN: r238307