Fix separate git-dir handling

.git can be a file that contains actual git-dir.
crup-runner couldn't handle this case as managed checkout.

Review URL: https://codereview.chromium.org/84543002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@237074 0039d316-1c4b-4281-b951-d872f2087c98

crup-runner.sh

@@ -90,7 +90,8 @@ cd "$solution" 1>/dev/null
 
 if [ "$solution" = "$1" ]; then
   # Skip git checkouts not managed by crup.
-  if ! grep -q -s "The Chromium Authors" ".git/description"; then
+  gitdir="$(git rev-parse --git-dir)"
+  if ! grep -q -s "The Chromium Authors" "$gitdir/description"; then
     echo "Skipping unmanaged git directory $1" 1>&2
     exit 0
   fi