libstdc++-v3/ChangeLog:

	PR libstdc++/99058
	* doc/xml/manual/status_cxx2011.xml: Document when support
	became stable.
	* doc/xml/manual/status_cxx2014.xml: Likewise.
	* doc/xml/manual/status_cxx2017.xml: Likewise.
	* doc/html/manual/status.html: Regenerate.

Tested powerpc64le-linux. Committed to trunk.