dawn/cmake: fix DAWN_USE_BUILT_DXC define not being enabled in dawn_native_objects

Since the following CL landed, DAWN_USE_BUILT_DXC was not enabled for
the source files defined in the "dawn_native_objects" CMake list:
https://dawn-review.googlesource.com/c/dawn/+/194920

As a result, `use_dxc` was not enabled by default, among other things.

Change-Id: Ic48e6911cdd95bdacfaf0f44c4d04785d126ba4a
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/213295
Auto-Submit: Antonio Maiorano <amaiorano@google.com>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/dawn/native/CMakeLists.txt b/src/dawn/native/CMakeLists.txt
index be4aeff..1bcb6b2 100644
--- a/src/dawn/native/CMakeLists.txt
+++ b/src/dawn/native/CMakeLists.txt
@@ -850,6 +850,7 @@
 if (DAWN_ENABLE_D3D12)
     if (DAWN_USE_BUILT_DXC)
         target_compile_definitions(dawn_native PRIVATE "DAWN_USE_BUILT_DXC")
+        target_compile_definitions(dawn_native_objects PRIVATE "DAWN_USE_BUILT_DXC")
         add_dependencies(dawn_native copy_dxil_dll)
     endif()
 endif()