[libcxx] [test] Need to include <string> for its streaming operators.

[STL_MSFT]

Summary

[libcxx] [test] Need to include <string> for its streaming operators.

Fixes MSVC errors:
"error C2678: binary '>>': no operator found which takes a left-hand operand of type 'std::istrstream' (or there is no acceptable conversion)"
"error C2679: binary '<<': no operator found which takes a right-hand operand of type 'std::string' (or there is no acceptable conversion)"

[EricWF]

r267959.

test/std/depr/depr.str.strstreams/depr.istrstream/depr.istrstream.cons/ccp.pass.cpp

 // <strstream>
 
 // class istrstream
 
 // explicit istrstream(const char* s);
 
 #include <strstream>
 #include <cassert>
+#include <string>
 
 int main()
 {
     {
         const char buf[] = "123 4.5 dog";
         std::istrstream in(buf);
         int i;
         in >> i;

test/std/depr/depr.str.strstreams/depr.istrstream/depr.istrstream.cons/ccp_size.pass.cpp

 // <strstream>
 
 // class istrstream
 
 // explicit istrstream(const char* s, streamsize n);
 
 #include <strstream>
 #include <cassert>
+#include <string>
 
 int main()
 {
     {
         const char buf[] = "123 4.5 dog";
         std::istrstream in(buf, 7);
         int i;
         in >> i;

test/std/depr/depr.str.strstreams/depr.istrstream/depr.istrstream.cons/cp.pass.cpp

 // <strstream>
 
 // class istrstream
 
 // explicit istrstream(char* s);
 
 #include <strstream>
 #include <cassert>
+#include <string>
 
 int main()
 {
     {
         char buf[] = "123 4.5 dog";
         std::istrstream in(buf);
         int i;
         in >> i;

test/std/depr/depr.str.strstreams/depr.istrstream/depr.istrstream.cons/cp_size.pass.cpp

 // <strstream>
 
 // class istrstream
 
 // explicit istrstream(char* s, streamsize n);
 
 #include <strstream>
 #include <cassert>
+#include <string>
 
 int main()
 {
     {
         char buf[] = "123 4.5 dog";
         std::istrstream in(buf, 7);
         int i;
         in >> i;

test/std/depr/depr.str.strstreams/depr.ostrstream/depr.ostrstream.cons/cp_size_mode.pass.cpp

 // <strstream>
 
 // class ostrstream
 
 // ostrstream(char* s, int n, ios_base::openmode mode = ios_base::out);
 
 #include <strstream>
 #include <cassert>
+#include <string>
 
 int main()
 {
     {
         char buf[] = "123 4.5 dog";
         std::ostrstream out(buf, 0);
         assert(out.str() == std::string("123 4.5 dog"));
         int i = 321;

test/std/depr/depr.str.strstreams/depr.ostrstream/depr.ostrstream.cons/default.pass.cpp

 // <strstream>
 
 // class ostrstream
 
 // ostrstream();
 
 #include <strstream>
 #include <cassert>
+#include <string>
 
 int main()
 {
     std::ostrstream out;
     int i = 123;
     double d = 4.5;
     std::string s("dog");
     out << i << ' ' << d << ' ' << s << std::ends;
     assert(out.str() == std::string("123 4.5 dog"));
     out.freeze(false);
 }

test/std/depr/depr.str.strstreams/depr.strstream/depr.strstream.cons/cp_size_mode.pass.cpp

 // <strstream>
 
 // class strstream
 
 // strstream(char* s, int n, ios_base::openmode mode = ios_base::in | ios_base::out);
 
 #include <strstream>
 #include <cassert>
+#include <string>
 
 int main()
 {
     {
         char buf[] = "123 4.5 dog";
         std::strstream inout(buf, 0);
         assert(inout.str() == std::string("123 4.5 dog"));
         int i = 321;

test/std/depr/depr.str.strstreams/depr.strstream/depr.strstream.cons/default.pass.cpp

 // <strstream>
 
 // class strstream
 
 // strstream();
 
 #include <strstream>
 #include <cassert>
+#include <string>
 
 int main()
 {
     std::strstream inout;
     int i = 123;
     double d = 4.5;
     std::string s("dog");
     inout << i << ' ' << d << ' ' << s << std::ends;