Fix build of tests with libc++

- The exclusive_scan fallback for libstdc++ < 9 was selected by mistake
  (GLIBCXX_RELEASE instead of _GLIBCXX_RELEASE), and not defined without
  libstdc++.
- sparse_matrix.hpp has a global "using namespace std", which makes __all
  in the HIP headers ambiguous with std::__all from libc++. Include it
  after the HIP headers.
--- a/test/hipcub/test_hipcub_block_radix_rank.cpp
+++ b/test/hipcub/test_hipcub_block_radix_rank.cpp
@@ -605,7 +605,7 @@ void rank_with_prefix_sum_kernel(const KeyType* keys_input,
     }
 }
 
-#if defined(_GLIBCXX_RELEASE) && (GLIBCXX_RELEASE < 9)
+#if defined(_GLIBCXX_RELEASE) && (_GLIBCXX_RELEASE < 9)
 
 /**
  * name this function fall_back_exclusive_scan to prevent
@@ -722,7 +722,7 @@ void test_radix_rank_with_prefix_sum_output()
 
                     ++histogram[bit_rep];
                 }
-                #if defined(_WIN32) || (defined(_GLIBCXX_RELEASE) && (GLIBCXX_RELEASE >= 9))
+                #if !defined(_GLIBCXX_RELEASE) || (_GLIBCXX_RELEASE >= 9)
                     std::exclusive_scan(histogram.begin(),
                                         histogram.end(),
                                         pfs_expected.begin() + pfs_offset,
--- a/test/hipcub/test_hipcub_device_spmv.cpp
+++ b/test/hipcub/test_hipcub_device_spmv.cpp
@@ -20,14 +20,15 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include "experimental/sparse_matrix.hpp"
-
 #include <hipcub/device/device_spmv.hpp>
 #include <hipcub/util_allocator.hpp>
 
 #include "common_test_header.hpp"
 #include "test_utils_assertions.hpp"
 
+// after the HIP headers: it has a global "using namespace std"
+#include "experimental/sparse_matrix.hpp"
+
 hipcub::CachingDeviceAllocator g_allocator;
 
 static constexpr float alpha_const = 1.0f;