More correctly detect the presence of aligned/sized new/delete.

This fixes a problem with the interaction of Clang and libstdc++'s
operator new overloads.

Also do some drive-by fixes to make sure everything compiles cleanly
with Clang and C++17.

Bug 2843412

Author: griwes

testing/scan.cu

@@ -2,6 +2,7 @@
 #include <thrust/scan.h>
 #include <thrust/functional.h>
 #include <thrust/iterator/discard_iterator.h>
+#include <thrust/iterator/constant_iterator.h>
 #include <thrust/iterator/retag.h>
 #include <thrust/device_malloc.h>
 #include <thrust/device_free.h>

thrust/device_new_allocator.h

@@ -139,6 +139,7 @@ template<typename T>
     inline void deallocate(pointer p, size_type cnt)
     {
       // use "::operator delete" rather than keyword delete
+      (void)cnt;
       device_delete(p);
     } // end deallocate()
 

thrust/mr/new.h

@@ -40,7 +40,7 @@ class new_delete_resource THRUST_FINAL : public memory_resource<>
 public:
     void * do_allocate(std::size_t bytes, std::size_t alignment = THRUST_MR_DEFAULT_ALIGNMENT) THRUST_OVERRIDE
     {
-#if __cplusplus >= 201703L
+#if defined(__cpp_aligned_new)
         return ::operator new(bytes, std::align_val_t(alignment));
 #else
         // allocate memory for bytes, plus potential alignment correction,
@@ -61,8 +61,13 @@ class new_delete_resource THRUST_FINAL : public memory_resource<>
 
     void do_deallocate(void * p, std::size_t bytes, std::size_t alignment = THRUST_MR_DEFAULT_ALIGNMENT) THRUST_OVERRIDE
     {
-#if __cplusplus >= 201703L
+#if defined(__cpp_aligned_new)
+# if defined(__cpp_sized_deallocation)
         ::operator delete(p, bytes, std::align_val_t(alignment));
+# else
+        (void)bytes;
+        ::operator delete(p, std::align_val_t(alignment));
+# endif
 #else
         (void)alignment;
         char * ptr = static_cast<char *>(p);