PR libstdc++/69413
	* config/os/gnu-linux/os_defines.h: Define
	_GLIBCXX_NO_OBSOLETE_ISINF_ISNAN_DYNAMIC.
	* include/c_global/cmath (isinf, isnan): Check it.
	* doc/xml/manual/internals.xml: Document it.
	* doc/html/*: Regenerate.

From-SVN: r232726