PR libstdc++/71856
	* doc/xml/manual/using.xml: Document macro.
	* include/bits/c++config [_GLIBCXX_DEBUG || _GLIBCXX_PARALLEL]
	(__glibcxx_assert): Rename to __glibcxx_assert_impl.
	[_GLIBCXX_DEBUG] (__glibcxx_assert): Expand to __glibcxx_assert_impl.
	* include/parallel/base.h [_GLIBCXX_PARALLEL_ASSERTIONS]
	(_GLIBCXX_PARALLEL_ASSERT): Expand to __glibcxx_assert_impl.
	[!_GLIBCXX_PARALLEL_ASSERTIONS] (_GLIBCXX_PARALLEL_ASSERT): Define as
	empty.
	* testsuite/25_algorithms/headers/algorithm/
	parallel_algorithm_assert2.cc: New test.

From-SVN: r243434