Cirrus: Tolerate missing projects when unpacking Git

tools/cirrus_unpack_git.sh

@@ -5,6 +5,16 @@ shopt -s failglob
 
 for PROJECT in ./git_index/*
 do
-    PROJECT_BASE=$(basename $PROJECT)
-    mv ${PROJECT} ./git_clones/${PROJECT_BASE}/.git/index
+    PROJECT_BASE="$(basename $PROJECT)"
+
+    # It's possible that the cache contains a project that was removed from the
+    # build sometime after the cache was saved.  In such a case, unpacking it
+    # would result in "No such file or directory", so we just discard it
+    # instead.
+    if [[ -d "./git_clones/${PROJECT_BASE}/.git" ]]
+    then
+        mv "${PROJECT}" "./git_clones/${PROJECT_BASE}/.git/index"
+    else
+        rm "${PROJECT}"
+    fi
 done