[libc][fix] Call GPU destructors in the correct order

Summary:
I was mistakenly iterating the list backwards. Regular semantics puts
both arrays in priority order but the destructors are called backwards.

Author: jhuber6

libc/startup/gpu/amdgpu/start.cpp

@@ -37,8 +37,8 @@ static void call_init_array_callbacks(int argc, char **argv, char **env) {
 
 static void call_fini_array_callbacks() {
   size_t fini_array_size = __fini_array_end - __fini_array_start;
-  for (size_t i = 0; i < fini_array_size; ++i)
-    reinterpret_cast<FiniCallback *>(__fini_array_start[i])();
+  for (size_t i = fini_array_size; i > 0; --i)
+    reinterpret_cast<FiniCallback *>(__fini_array_start[i - 1])();
 }
 
 } // namespace LIBC_NAMESPACE

libc/startup/gpu/nvptx/start.cpp

@@ -35,8 +35,8 @@ static void call_init_array_callbacks(int argc, char **argv, char **env) {
 
 static void call_fini_array_callbacks() {
   size_t fini_array_size = __fini_array_end - __fini_array_start;
-  for (size_t i = 0; i < fini_array_size; ++i)
-    reinterpret_cast<FiniCallback *>(__fini_array_start[i])();
+  for (size_t i = fini_array_size; i > 0; --i)
+    reinterpret_cast<FiniCallback *>(__fini_array_start[i - 1])();
 }
 
 } // namespace LIBC_NAMESPACE

libc/utils/gpu/loader/nvptx/Loader.cpp

@@ -83,7 +83,6 @@ Expected<void *> get_ctor_dtor_array(const void *image, const size_t size,
   // for destructors.
   llvm::sort(ctors, [](auto x, auto y) { return x.second < y.second; });
   llvm::sort(dtors, [](auto x, auto y) { return x.second < y.second; });
-  llvm::reverse(dtors);
 
   // Allocate host pinned memory to make these arrays visible to the GPU.
   CUdeviceptr *dev_memory = reinterpret_cast<CUdeviceptr *>(allocator(