Revert "Remove unused file and use the rules_rust transition allowlist. (bazelbuild#1182)"

This reverts commit 348c3e3.

Author: korDen

rust/private/transitions.bzl

@@ -105,7 +105,7 @@ without_process_wrapper = rule(
             executable = True,
         ),
         "_allowlist_function_transition": attr.label(
-            default = Label("//tools/allowlists/function_transition_allowlist"),
+            default = Label("@bazel_tools//tools/allowlists/function_transition_allowlist"),
         ),
     },
 )

util/process_wrapper/process_wrapper_fake.cc

@@ -0,0 +1,4 @@
+int main() {
+    // Noop on purpose.
+    return 0;
+}