PR libstdc++/85831
	* config/abi/pre/gnu.ver: Export move constructors and move
	assignment operators for std::logic_error and std::runtime_error.
	* include/std/stdexcept: Use _GLIBCXX_NOTHROW instead of
	_GLIBCXX_USE_NOEXCEPT.
	(logic_error, runtime_error): Declare move constructors and move
	assignment operators. When not declared already, define copy
	constructors and copy assignment operators as explicit-defaulted.
	(domain_error, invalid_argument, length_error, out_of_range)
	(overflow_error, underflow_error): Define move constructors and move
	assignment operators as explicitly-defaulted.
	* libsupc++/exception.h (exception): Likewise.
	* src/c++11/cow-stdexcept.cc (logic_error, runtime_error): Define
	move constructors and move assignment operators as defaulted.
	* testsuite/19_diagnostics/stdexcept.cc: Check that constructors and
	assignment operators are defined.

From-SVN: r262456