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/pow/f37b25.wgsl.expected.dxc.hlsl b/test/tint/builtins/gen/literal/pow/f37b25.wgsl.expected.dxc.hlsl
index e2d71b3..8cca74f 100644
--- a/test/tint/builtins/gen/literal/pow/f37b25.wgsl.expected.dxc.hlsl
+++ b/test/tint/builtins/gen/literal/pow/f37b25.wgsl.expected.dxc.hlsl
@@ -1,5 +1,8 @@
+RWByteAddressBuffer prevent_dce : register(u0, space2);
+
 void pow_f37b25() {
   vector<float16_t, 2> res = (float16_t(1.0h)).xx;
+  prevent_dce.Store<vector<float16_t, 2> >(0u, res);
 }
 
 struct tint_symbol {