Revert "Use upstream SPIRV-Cross GN files."

This reverts commit 9fdbb74072.

Reason for revert: The SPIRV-Cross GN files have a bug which is fixed upstream, but Skia is on an old version of SPIRV-Cross so they don't have the fix. So, the build fails when rolling Dawn into Skia complaining about unknown `-fno-exceptions` on the windows bots. Need Skia to either move to vulkan-deps, or roll their spirv-cross forward before this can re-land.

Original change's description:
> Use upstream SPIRV-Cross GN files.
>
> Previously spirv-cross didn't have its own sources files but this
> changed recently so we should use them. This will ultimately allow
> sharing targets between multiple components in Chromium.
>
> Bug: chromium:1179277
> Change-Id: Ib4bb1884b9ba9c4c3804e96d8adbb8905c60c9a3
> Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/41725
> Auto-Submit: Corentin Wallez <cwallez@chromium.org>
> Reviewed-by: Peng Huang <penghuang@chromium.org>
> Reviewed-by: Austin Eng <enga@chromium.org>
> Commit-Queue: Corentin Wallez <cwallez@chromium.org>

Bug: chromium:1179277
Change-Id: If1003bafa7b35f502c08b2dab91dd3d416aab077
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/42420
Commit-Queue: dan sinclair <dsinclair@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>
Auto-Submit: dan sinclair <dsinclair@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>

src/dawn_native/BUILD.gn

@@ -143,7 +143,7 @@ source_set("dawn_native_sources") {
     ":dawn_native_headers",
     ":dawn_native_utils_gen",
     "${dawn_root}/src/common",
-    "${dawn_spirv_cross_dir}/gn:spirv_cross_sources",
+    "${dawn_root}/third_party/gn/spirv_cross:spirv_cross",
     "${dawn_spirv_tools_dir}:spvtools_opt",
     "${dawn_spirv_tools_dir}:spvtools_val",
   ]