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/var/insertBits/428b0b.wgsl.expected.wgsl b/test/tint/builtins/gen/var/insertBits/428b0b.wgsl.expected.wgsl
index d9a37dc..347f19e 100644
--- a/test/tint/builtins/gen/var/insertBits/428b0b.wgsl.expected.wgsl
+++ b/test/tint/builtins/gen/var/insertBits/428b0b.wgsl.expected.wgsl
@@ -4,8 +4,11 @@
   var arg_2 = 1u;
   var arg_3 = 1u;
   var res : vec3<i32> = insertBits(arg_0, arg_1, arg_2, arg_3);
+  prevent_dce = res;
 }
 
+@group(2) @binding(0) var<storage, read_write> prevent_dce : vec3<i32>;
+
 @vertex
 fn vertex_main() -> @builtin(position) vec4<f32> {
   insertBits_428b0b();