Fix path for stamp file in fuzzer corpuse generation

BUG=chromium:1314527

Change-Id: I05adbe671c4f30fe3e59829cd370a59347c8ed51
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/86760
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Auto-Submit: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>

src/tint/fuzzers/BUILD.gn

diff --git a/src/tint/fuzzers/BUILD.gn b/src/tint/fuzzers/BUILD.gn
index afd1e3a..0934ab2 100644
--- a/src/tint/fuzzers/BUILD.gn
+++ b/src/tint/fuzzers/BUILD.gn
@@ -27,7 +27,7 @@
     script = "generate_wgsl_corpus.py"
     sources = [ "generate_wgsl_corpus.py" ]
     args = [
-      "--stamp=${fuzzer_corpus_wgsl_stamp}",
+      "--stamp=" + rebase_path(fuzzer_corpus_wgsl_stamp, root_build_dir),
       rebase_path("${tint_root_dir}/test", root_build_dir),
       rebase_path(fuzzer_corpus_wgsl_dir, root_build_dir),
     ]