libstdc++: Correct notes about std::call_once in manual [PR66146]

libstdc++: Correct notes about std::call_once in manual [PR66146]

The bug with exceptions thrown during a std::call_once call affects all
targets, so fix the docs that say it only affects non-Linux targets.

libstdc++-v3/ChangeLog:

	PR libstdc++/66146
	* doc/xml/manual/status_cxx2011.xml: Remove mention of Linux in
	note about std::call_once.
	* doc/xml/manual/status_cxx2014.xml: Likewise.
	* doc/xml/manual/status_cxx2017.xml: Likewise.
	* doc/html/manual/status.html: Regenerate.

(cherry picked from commit e6836bbbd7a01af0791c02087e568b4822418c0d)