Allow /usr/crosstool to exist in EdgeOS builds

BUG=b/290986313
TEST=Built a VM image with this and didn't get shot down by hook script
RELEASE_NOTE=None

Change-Id: I3b3256668dc5a600adadacc89ac6bbe5e066b194
Reviewed-on: https://cos-review.googlesource.com/c/third_party/platform/crosutils/+/62574
Reviewed-by: Alan Berryhill <berryhill@google.com>
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
diff --git a/hooks/filesystem-layout.py b/hooks/filesystem-layout.py
index 111cd15..295ff86 100755
--- a/hooks/filesystem-layout.py
+++ b/hooks/filesystem-layout.py
@@ -89,6 +89,7 @@
 VALID_HOST_USR = set()
 
 VALID_EDGEOS_USR = {
+    "crosstool",
     "grte",
 }