libstdc++: testsuite: work around bitset namespace pollution

rtems6 declares a global struct bitset in a header file included
indirectly by sys/types.h, that ambiguates the unqualified references
to bitset after "using namespace std" in the testsuite.

Work around the namespace pollution with using declarations of
std::bitset.


for  libstdc++-v3/ChangeLog

	* testsuite/23_containers/bitset/cons/dr1325-2.cc: Work around
	global struct bitset.
	* testsuite/23_containers/bitset/ext/15361.cc: Likewise.
	* testsuite/23_containers/bitset/input/1.cc: Likewise.
	* testsuite/23_containers/bitset/to_string/1.cc: Likewise.
	* testsuite/23_containers/bitset/to_string/dr396.cc: Likewise.

libstdc++-v3/testsuite/23_containers/bitset/cons/dr1325-2.cc

@@ -39,6 +39,7 @@ template<std::size_t Nb, typename CharT>
 void test01()
 {
   using namespace std;
+  using std::bitset; // Work around struct ::bitset on rtems.
 
   const char s1[4] = { '0', '1', '0', '1' };
   VERIFY( bitset<4>(s1, 4) == test01_ref<4>(s1, 4) );

libstdc++-v3/testsuite/23_containers/bitset/ext/15361.cc

@@ -22,6 +22,7 @@
 void test01()
 {
   using namespace std;
+  using std::bitset; // Work around struct ::bitset on rtems.
 
   bitset<256> b;
   b.set(225);

libstdc++-v3/testsuite/23_containers/bitset/input/1.cc

@@ -26,6 +26,7 @@
 void test01()
 {
   using namespace std;
+  using std::bitset; // Work around struct ::bitset on rtems.
 
   bitset<5>      b5;
   bitset<0>      b0;

libstdc++-v3/testsuite/23_containers/bitset/to_string/1.cc

@@ -25,6 +25,7 @@
 void test01()
 {
   using namespace std;
+  using std::bitset; // Work around struct ::bitset on rtems.
 
   bitset<5> b5;
   string s0 = b5.to_string<char, char_traits<char>, allocator<char> >();

libstdc++-v3/testsuite/23_containers/bitset/to_string/dr396.cc

@@ -26,6 +26,7 @@
 void test01()
 {
   using namespace std;
+  using std::bitset; // Work around struct ::bitset on rtems.
 
   bitset<5> b5;
   string s0 = b5.to_string<char, char_traits<char>, allocator<char> >('a', 'b');