Make: Retool how we cache go dirs

Now we can use /dev/null as an argument when running tools manually

hack/make-rules/helpers/cache_go_dirs.sh

@@ -54,19 +54,19 @@ function kfind() {
         | sed 's|^./staging/src|vendor|'
 }
 
-NEED_FIND=true
 # It's *significantly* faster to check whether any directories are newer than
 # the cache than to blindly rebuild it.
-if [[ -f "${CACHE}" ]]; then
+if [[ -f "${CACHE}" && -n "${CACHE}" ]]; then
     N=$(kfind -type d -newer "${CACHE}" -print -quit | wc -l)
-    [[ "${N}" == 0 ]] && NEED_FIND=false
+    if [[ "${N}" == 0 ]]; then
+        cat "${CACHE}"
+        exit
+    fi
 fi
+
 mkdir -p "$(dirname "${CACHE}")"
-if ${NEED_FIND}; then
-    kfind -type f -name \*.go  \
-        | sed 's|/[^/]*$||'    \
-        | sed 's|^./||'        \
-        | LC_ALL=C sort -u     \
-        > "${CACHE}"
-fi
-cat "${CACHE}"
+kfind -type f -name \*.go  \
+    | sed 's|/[^/]*$||'    \
+    | sed 's|^./||'        \
+    | LC_ALL=C sort -u     \
+    | tee "${CACHE}"