test/tint/builtins/gen: Use returned value

It appears that FXC and DXC do some validation post dead-code-elimination.
These tests have been updated so that the return value is assigned to a storage buffer, ensuring that all validation is performed.

Many DXC tests are affected by https://github.com/microsoft/DirectXShaderCompiler/issues/5082, which have been SKIP'ed.

Fixed: tint:1859
Change-Id: I0001a9a9821846cd0855c3d8ce2bec79ab8e64ef
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/122662
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: James Price <jrprice@google.com>
Commit-Queue: James Price <jrprice@google.com>
Auto-Submit: Ben Clayton <bclayton@google.com>
diff --git a/test/tint/builtins/gen/literal/atomicAdd/d5db1d.wgsl b/test/tint/builtins/gen/literal/atomicAdd/d5db1d.wgsl
index 93a8c26..07c33aa 100644
--- a/test/tint/builtins/gen/literal/atomicAdd/d5db1d.wgsl
+++ b/test/tint/builtins/gen/literal/atomicAdd/d5db1d.wgsl
@@ -25,7 +25,9 @@
 // fn atomicAdd(ptr<workgroup, atomic<u32>, read_write>, u32) -> u32
 fn atomicAdd_d5db1d() {
   var res: u32 = atomicAdd(&arg_0, 1u);
+  prevent_dce = res;
 }
+@group(2) @binding(0) var<storage, read_write> prevent_dce : u32;
 
 @compute @workgroup_size(1)
 fn compute_main() {