[gn] Disable fuzzers when '[dawn|tint]_has_build' is false

Change-Id: Icd8521e0021ea59af9dcad83521fa608c3ee08b7
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/154541
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: dan sinclair <dsinclair@chromium.org>
Kokoro: Ben Clayton <bclayton@google.com>
diff --git a/build_overrides/tint.gni b/build_overrides/tint.gni
index 7d5af1a..46355c8 100644
--- a/build_overrides/tint.gni
+++ b/build_overrides/tint.gni
@@ -12,6 +12,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+# True if Tint can access build/, testing/ and other Chrome folders.
+tint_has_build = true
+
 tint_spirv_tools_dir = "//third_party/vulkan-deps/spirv-tools/src"
 tint_spirv_headers_dir = "//third_party/vulkan-deps/spirv-headers/src"
 tint_glslang_dir = "//third_party/vulkan-deps/glslang/src"