libstdc++: Fix tests that fail in C++98 mode

libstdc++: Fix tests that fail in C++98 mode

The header synopsis test fails to define NOTHROW for C++98.

The shared_ptr test should be skipped for C++98.

The debug mode one should work for C++98 too, it just needs to avoid
C++11 syntax that isn't valid in C++98.

libstdc++-v3/ChangeLog:

	* testsuite/20_util/headers/memory/synopsis.cc: Define C++98
	alternative for macro.
	* testsuite/20_util/shared_ptr/creation/99006.cc: Add effective
	target keyword.
	* testsuite/25_algorithms/copy/debug/99402.cc: Avoid C++11
	syntax.

(cherry picked from commit 37407a2ae701c0a93377106a2938ab5474062fc3)