gn: Add empty ubsan ignore list

Required to build Dawn with GN flag `is_ubsan = true`

Change-Id: I80b49b81377f0a9c8bd2c1310e12786427947c38
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/95760
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
diff --git a/tools/ubsan/ignorelist.txt b/tools/ubsan/ignorelist.txt
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/tools/ubsan/ignorelist.txt