Revert "Use constexpr if in case it's available"

This reverts commit 91d5e6c.

Author: alliepiper

thrust/system/cuda/detail/sort.h

@@ -49,7 +49,6 @@
 #include <thrust/detail/alignment.h>
 #include <thrust/type_traits/is_contiguous_iterator.h>
 
-
 THRUST_NAMESPACE_BEGIN
 namespace cuda_cub {
 
@@ -73,63 +72,59 @@ namespace __merge_sort {
   {
     (void)items;
 
-    cudaError_t status = cudaSuccess;
-
     if (keys_count == 0)
     {
-      return status;
+      return cudaSuccess;
     }
 
-    THRUST_IF_CONSTEXPR(STABLE::value)
+    if (STABLE::value)
     {
-      THRUST_IF_CONSTEXPR(SORT_ITEMS::value)
+      if (SORT_ITEMS::value)
       {
-        status = cub::DeviceMergeSort::StableSortPairs(d_temp_storage,
-                                                       temp_storage_bytes,
-                                                       keys,
-                                                       items,
-                                                       keys_count,
-                                                       compare_op,
-                                                       stream,
-                                                       debug_sync);
+        return cub::DeviceMergeSort::StableSortPairs(d_temp_storage,
+                                                     temp_storage_bytes,
+                                                     keys,
+                                                     items,
+                                                     keys_count,
+                                                     compare_op,
+                                                     stream,
+                                                     debug_sync);
       }
       else
       {
-        status = cub::DeviceMergeSort::StableSortKeys(d_temp_storage,
-                                                      temp_storage_bytes,
-                                                      keys,
-                                                      keys_count,
-                                                      compare_op,
-                                                      stream,
-                                                      debug_sync);
+        return cub::DeviceMergeSort::StableSortKeys(d_temp_storage,
+                                                    temp_storage_bytes,
+                                                    keys,
+                                                    keys_count,
+                                                    compare_op,
+                                                    stream,
+                                                    debug_sync);
       }
     }
     else
     {
-      THRUST_IF_CONSTEXPR(SORT_ITEMS::value)
+      if (SORT_ITEMS::value)
       {
-        status = cub::DeviceMergeSort::SortPairs(d_temp_storage,
-                                                 temp_storage_bytes,
-                                                 keys,
-                                                 items,
-                                                 keys_count,
-                                                 compare_op,
-                                                 stream,
-                                                 debug_sync);
+        return cub::DeviceMergeSort::SortPairs(d_temp_storage,
+                                               temp_storage_bytes,
+                                               keys,
+                                               items,
+                                               keys_count,
+                                               compare_op,
+                                               stream,
+                                               debug_sync);
       }
       else
       {
-        status = cub::DeviceMergeSort::SortKeys(d_temp_storage,
-                                                temp_storage_bytes,
-                                                keys,
-                                                keys_count,
-                                                compare_op,
-                                                stream,
-                                                debug_sync);
+        return cub::DeviceMergeSort::SortKeys(d_temp_storage,
+                                              temp_storage_bytes,
+                                              keys,
+                                              keys_count,
+                                              compare_op,
+                                              stream,
+                                              debug_sync);
       }
     }
-
-    return status;
   }
 
   template <typename SORT_ITEMS,