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.