Fix build of tint_cmd_helper

spvtools_headers are not available without tint_build_spv_writer

Change-Id: If4539715b0e685c9b54bf24719a905fb0265a402
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/122820
Commit-Queue: Austin Eng <enga@chromium.org>
Kokoro: Austin Eng <enga@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: James Price <jrprice@google.com>
diff --git a/src/tint/cmd/BUILD.gn b/src/tint/cmd/BUILD.gn
index ab0c964..e9188cf 100644
--- a/src/tint/cmd/BUILD.gn
+++ b/src/tint/cmd/BUILD.gn
@@ -21,10 +21,10 @@
     "helper.h",
   ]
 
-  deps = [
-    "${tint_root_dir}/src/tint:libtint",
-    "${tint_spirv_tools_dir}/:spvtools_headers",
-  ]
+  deps = [ "${tint_root_dir}/src/tint:libtint" ]
+  if (tint_build_spv_writer) {
+    deps += [ "${tint_spirv_tools_dir}/:spvtools_headers" ]
+  }
 }
 
 executable("tint") {