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.

libstdc++-v3/testsuite/20_util/headers/memory/synopsis.cc

@@ -22,6 +22,8 @@
 
 #if __cplusplus >= 201103L
 # define NOTHROW noexcept
+#else
+# define NOTHROW
 #endif
 
 namespace std {

libstdc++-v3/testsuite/20_util/shared_ptr/creation/99006.cc

@@ -1,5 +1,5 @@
-// FIXME: This should use { target { ! c++20 } }
-// { dg-do compile }
+// FIXME: This should use { target { c++11 && { ! c++20 } } }
+// { dg-do compile { target { c++11 } } }
 
 #include <memory>
 

libstdc++-v3/testsuite/25_algorithms/copy/debug/99402.cc

@@ -28,8 +28,9 @@ using namespace std;
 
 int main()
 {
+    int two[] = { 0, 1 };
     // any container with non-random access iterators:
-    const set<int> source = { 0, 1 };
+    const set<int> source(two, two + 2);
     vector<int> dest(1);
     copy(source.begin(), ++source.begin(), dest.begin());
 }